Update F# formatting sample

[cartermp]

Make it correct w.r.t the document

[cartermp]

dotnet/docs#6261

[cartermp]

@dend any idea why the CI is failing?

[mairaw]

Looking at the output, it might be missing the required .NET Framework SDK:

2018-07-02T16:52:54.1714125Z   Restore completed in 58.08 ms for /samples/roslyn-sdk/SyntaxQuickStart/SyntaxWalker/SyntaxWalker.csproj.
2018-07-02T16:52:54.4129065Z /usr/share/dotnet/sdk/2.1.301/Microsoft.Common.CurrentVersion.targets(1179,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v4.6.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [/samples/roslyn-sdk/SyntaxQuickStart/SyntaxWalker/SyntaxWalker.csproj]
2018-07-02T16:52:54.4294526Z 
2018-07-02T16:52:54.4317446Z Build FAILED.
2018-07-02T16:52:54.4326706Z 
2018-07-02T16:52:54.4355555Z /usr/share/dotnet/sdk/2.1.301/Microsoft.Common.CurrentVersion.targets(1179,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v4.6.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [/samples/roslyn-sdk/SyntaxQuickStart/SyntaxWalker/SyntaxWalker.csproj]
2018-07-02T16:52:54.4386973Z     0 Warning(s)
2018-07-02T16:52:54.4407817Z     1 Error(s)
2018-07-02T16:52:54.4415431Z 
2018-07-02T16:52:54.4430974Z Time Elapsed 00:00:01.15
2018-07-02T16:52:55.7552664Z   Restoring packages for /samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/HelloSyntaxTree.csproj...
2018-07-02T16:52:56.1440071Z   Generating MSBuild file /samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/obj/HelloSyntaxTree.csproj.nuget.g.props.
2018-07-02T16:52:56.1469604Z   Generating MSBuild file /samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/obj/HelloSyntaxTree.csproj.nuget.g.targets.
2018-07-02T16:52:56.1493338Z   Restore completed in 386.9 ms for /samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/HelloSyntaxTree.csproj.
2018-07-02T16:52:56.4943894Z Microsoft (R) Build Engine version 15.7.179.6572 for .NET Core
2018-07-02T16:52:56.4959885Z Copyright (C) Microsoft Corporation. All rights reserved.
2018-07-02T16:52:56.4968525Z 
2018-07-02T16:52:57.5188690Z   Restore completed in 55.19 ms for /samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/HelloSyntaxTree.csproj.
2018-07-02T16:52:57.7294465Z /usr/share/dotnet/sdk/2.1.301/Microsoft.Common.CurrentVersion.targets(1179,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v4.6.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [/samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/HelloSyntaxTree.csproj]
2018-07-02T16:52:57.7508340Z 
2018-07-02T16:52:57.7533175Z Build FAILED.
2018-07-02T16:52:57.7541585Z 
2018-07-02T16:52:57.7569524Z /usr/share/dotnet/sdk/2.1.301/Microsoft.Common.CurrentVersion.targets(1179,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v4.6.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [/samples/roslyn-sdk/SyntaxQuickStart/HelloSyntaxTree/HelloSyntaxTree.csproj]
2018-07-02T16:52:57.7599913Z     0 Warning(s)
2018-07-02T16:52:57.7614882Z     1 Error(s)

[mairaw]

We've been merging as-is for now until we can figure out the CI story.

[cartermp]

Sounds good. @mairaw can you approve? I can't approve my own PR.