Fix greedy wsl detection (#612)

Author: SimonCropp

src/DiffEngine/BuildServerDetector.cs

@@ -43,7 +43,7 @@ static BuildServerDetector()
         // https://www.appveyor.com/docs/environment-variables/
         IsAppVeyor = variables.Contains("APPVEYOR");
 
-        IsWsl = variables.Contains("WSLENV");
+        IsWsl = variables.Contains("WSL_DISTRO_NAME");
 
         // AzureDevops
         // https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=azure-devops&tabs=yaml#agent-variables

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649</NoWarn>
-    <Version>15.10.0</Version>
+    <Version>15.10.1</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Testing, Snapshot, Diff, Compare</PackageTags>
     <Description>Launches diff tools based on file extensions. Designed to be consumed by snapshot testing libraries.</Description>