Use LangVersion 7.3 everywhere

Author: AArnott

src/Directory.Build.props

@@ -4,6 +4,7 @@
     <BaseIntermediateOutputPath>$(MSBuildThisFileDirectory)..\obj\$(MSBuildProjectName)\</BaseIntermediateOutputPath>
     <OutputPath>$(MSBuildThisFileDirectory)..\bin\$(MSBuildProjectName)\$(Configuration)\</OutputPath>
     <DocumentationRootFolder>$(MSBuildThisFileDirectory)..\wiki\api</DocumentationRootFolder>
+    <LangVersion>7.3</LangVersion>
 
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)strongname.snk</AssemblyOriginatorKeyFile>

src/nbgv/nbgv.csproj

@@ -6,7 +6,6 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <RootNamespace>Nerdbank.GitVersioning.Tool</RootNamespace>
-    <LangVersion>7.3</LangVersion>
     <Description>A .NET Core Tool that can install, read and set version information based on git history, using Nerdbank.GitVersioning.</Description>
   </PropertyGroup>