Fix accidental tabs

Author: jnm2

src/Directory.Build.props

@@ -1,20 +1,20 @@
 <Project>
 
   <PropertyGroup>
-	<TreatWarningsAsErrors Condition="'$(Configuration)' == 'Release'">true</TreatWarningsAsErrors>
+    <TreatWarningsAsErrors Condition="'$(Configuration)' == 'Release'">true</TreatWarningsAsErrors>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.435" PrivateAssets="all" />
   </ItemGroup>
 
   <PropertyGroup>
-	<ImplicitUsings>enable</ImplicitUsings>
+    <ImplicitUsings>enable</ImplicitUsings>
   </PropertyGroup>
   <ItemGroup>
     <Using Include="System.Collections.Immutable" />
     <Using Include="System.Diagnostics" />
-	<Using Include="System.Diagnostics.CodeAnalysis" />
+    <Using Include="System.Diagnostics.CodeAnalysis" />
   </ItemGroup>
 
 </Project>