Update CONTRIBUTING.MD
There was a typo in the file that was corrected. :)
@@ -30,7 +30,7 @@ habits of existing contributors. Drop by the #xi-editor stream on
signup), or the #xi channel on irc.mozilla.org, to follow ongoing discussions or
ask questions. Clone the repos you're interested in, and make sure you can build
and run the tests. If you can't, open an issue, and someone will try to help.
-Once you're up and running, there are a a number of ways to participate:
+Once you're up and running, there are a number of ways to participate:
### Opening issues
