Fix article in Index.rst (#374)

Author: stweil

Documentation/Troubleshooting/Index.rst

@@ -152,7 +152,7 @@ Push: invalid committer
    error: failed to push some refs to 'ssh://<username>@review.typo3.org:29418/REPOSITORY_NAME.git'
 
 
-This message simply means that your email address is not registered as an Web-Identity.
+This message simply means that your email address is not registered as a Web-Identity.
 If this error happens, just go to the website that the error message suggests:
 `https://review.typo3.org/#/settings/contact`. Register the email address you
 use to push (button :guilabel:`Register New Email`) - even if it is already in the dropdown list.