Bump StyleCop for better C#9 compatibility

Author: JimBobSquarePants

msbuild/props/SixLabors.Global.props

@@ -115,7 +115,10 @@
       PrivateAssets="All" Version="1.0.0"
       IsImplicitlyDefined="true"
       Condition="$(TargetFramework.StartsWith('net4'))"/>
-    <PackageReference Include="StyleCop.Analyzers" PrivateAssets="All" Version="1.1.118" IsImplicitlyDefined="true" />
+    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.354" IsImplicitlyDefined="true">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
     <AdditionalFiles Include="$(MSBuildThisFileDirectory)..\..\stylecop.json" />
   </ItemGroup>