Bump ReportGenerator from 4.7.1 to 4.8.0 (#428)

Author: dependabot[bot]

Directory.Build.targets

@@ -10,7 +10,7 @@
   <ItemGroup>
     <PackageReference Update="GitVersion.Tool" Version="5.5.0" />
     <PackageReference Update="JetBrains.ReSharper.CommandLineTools" Version="2020.2.4" />
-    <PackageReference Update="ReportGenerator" Version="4.7.1" />
+    <PackageReference Update="ReportGenerator" Version="4.8.0" />
     <PackageReference Update="Rocket.Surgery.Nuke" Version="0.14.0-beta.10" />
   </ItemGroup>
   <ItemGroup>