fix(validate-go): show the errors gofmt found

Rather than just listing files that have errors, this now shows
the diff of what gofmt things should be the case, and what is
the case.

scripts/validate-go.sh

@@ -48,6 +48,7 @@ if [[ -n "${failed_fmt}" ]]; then
   echo "${red}"
   echo "gofmt check failed:"
   echo "$failed_fmt"
+  find_go_files | xargs gofmt -s -d
   echo "${reset}"
   exit_code=1
 fi