Adding --no-author option to dzil test in GitGuide

Instead of making the users run author tests, and thus requiring them to
install more modules than necessary, they can specify the --no-author option
to skip these tests when testing Dancer2.

GitGuide.md

@@ -161,7 +161,7 @@ When that is done, you're good to go! You can use `dzil` to build and test
 Dancer2:
 
      $ dzil build
-     $ dzil test
+     $ dzil test --no-author
 
 
 ### Patch Submission (Github workflow)