Fix typo in CONTRIBUTING.md when checking committer permissions
# Contributing to Apache Ignite
-## Joining Community and it's communication channels
+## Joining Community and its communication channels
- Sign-in to Apache JIRA https://issues.apache.org/jira/
- (To contribute code patches) Sing-in to [Apache Ignite](https://ignite.apache.org/) Continuous Integration server https://ci.ignite.apache.org/
- (To contribute documentation to the wiki) Sing-in to [Apache Wiki](https://cwiki.apache.org/confluence/display/IGNITE)
