Update dependencies

Author: JimBobSquarePants

msbuild/props/SixLabors.Global.props

@@ -115,7 +115,7 @@
 
   <!-- Package references and additional files which are consumed by all projects. -->
   <ItemGroup>
-    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.507" IsImplicitlyDefined="true">
+    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556" IsImplicitlyDefined="true">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
     </PackageReference>

msbuild/props/SixLabors.Tests.props

@@ -11,7 +11,7 @@
 
   <!-- Package references and additional files which are consumed by test projects -->
   <ItemGroup Condition="'$(IsTestProject)' == 'true'">
-    <PackageReference Include="xunit" Version="2.6.2" IsImplicitlyDefined="true" />
+    <PackageReference Include="xunit" Version="2.6.5" IsImplicitlyDefined="true" />
 
     <PackageReference Include="coverlet.collector"
                       Version="6.0.0"
@@ -24,7 +24,7 @@
                       IsImplicitlyDefined="true"/>
 
     <PackageReference Include="xunit.runner.visualstudio"
-                      Version="2.5.4"
+                      Version="2.5.6"
                       IsImplicitlyDefined="true" />
 
     <Using Include="Xunit" Condition="'$(ImplicitUsings)'=='enable' OR '$(ImplicitUsings)'=='true'"/>