Update Roslyn to 2.3.1 (#1574)

Author: mikeharder

build/dependencies.props

@@ -11,7 +11,7 @@
     <NETStandardImplicitPackageVersion>2.0.0-*</NETStandardImplicitPackageVersion>
     <NETStandardLibraryNETFrameworkVersion>2.0.0-*</NETStandardLibraryNETFrameworkVersion>
     <RuntimeFrameworkVersion Condition="'$(TargetFramework)'=='netcoreapp2.0'">2.0.0-*</RuntimeFrameworkVersion>
-    <RoslynVersion>2.3.0</RoslynVersion>
+    <RoslynVersion>2.3.1</RoslynVersion>
     <RoslynDevVersion>2.6.0-beta*</RoslynDevVersion>
     <StreamJsonRpcVersion>1.1.92</StreamJsonRpcVersion>
     <TestSdkVersion>15.3.0-*</TestSdkVersion>