No bug: Don't generate trailing whitespace in `l10n-changesets.json`; r=aki

Differential Revision: https://phabricator.services.mozilla.com/D1536

--HG--
extra : moz-landing-system : lando

testing/mozharness/scripts/l10n_bumper.py

@@ -277,7 +277,10 @@ class L10nBumper(VCSScript):
                 continue
 
             # Write to disk
-            content_string = json.dumps(new_contents, sort_keys=True, indent=4)
+            content_string = json.dumps(
+                new_contents, sort_keys=True, indent=4,
+                separators=(',', ': '),
+            )
             fh = codecs.open(path, encoding='utf-8', mode='w+')
             fh.write(content_string + "\n")
             fh.close()