Fix link to TestStartInfo in test-protocol.md

[atifaziz]

Link to TestStartInfo in test protocol documentation page was broken (404). It points to:

https://github.com/dotnet/cli/blob/rel/1.0.0/src/dotnet/commands/dotnet-test/TestStartInfo.cs

The correct link, however, appears to be:

https://github.com/dotnet/cli/blob/rel/1.0.0/src/Microsoft.DotNet.Tools.Test/TestStartInfo.cs

This PR fixes that.

[dnfclas]

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[qinezh]

Open Publishing Build Service: The pull request content has been published and here are some changed files links of this time:

• Docset 1 - core-docs
  https://review.docs.microsoft.com/en-us/dotnet/articles/core/tools/test-protocol?branch=pr-en-us-1043

Status: Succeeded.
Open Publishing Report.

[mairaw]

Thanks @atifaziz! It seems they have changed the location of some source files recently.

[atifaziz]

It seems they have changed the location of some source files recently.

@mairaw Surprised though because the (old and new) links are off the 1.0.0 release tag so if moves happened after that then it shouldn't break anything, unless of course the tag was re-written.