fix(publish): add force flag for pub publish script

The pub publish process was not following through with publishing
packages because the -f flag was not be provided to pub publish,
causing the process to prompt for confirmation before publishing,
which was causing the pub_publish.sh script to skip publishing.

Closes angular#3077

Author: jeffbcross

scripts/publish/pub_publish.sh

@@ -34,7 +34,7 @@ function publishModule {
   node scripts/publish/pubspec_cleaner.js --pubspec-file=$PUBLISH_DIR/pubspec.yaml
 
   if [[ ! $DRY_RUN ]]; then
-    (cd $PUBLISH_DIR && pub publish)
+    (cd $PUBLISH_DIR && pub publish -f)
   fi;
 }