Merge pull request #101 from AArnott/fix100

Fix failing unit tests

Author: AArnott

src/Directory.Build.targets

@@ -7,7 +7,7 @@
     <PackageReference Update="CodeGeneration.Roslyn" Version="$(CodeGenerationRoslynVersion)" />
     <PackageReference Update="CodeGeneration.Roslyn.BuildTime" Version="$(CodeGenerationRoslynVersion)" />
     <PackageReference Update="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="2.9.0" />
-    <PackageReference Update="System.Collections.Immutable" Version="1.4.0" />
+    <PackageReference Update="System.Collections.Immutable" Version="1.5.0" />
     <PackageReference Update="Validation" Version="2.4.18" />
     <PackageReference Update="Microsoft.Build" Version="14.3.0" />
     <PackageReference Update="xunit" Version="2.3.1" />