Minor: Updated the Developer.md with recent move to gerrit.
Minor: Updated the Developer.md with recent move to gerrit.

hmcl/Streams,hortonworks/streamline,hmcl/Streams,hmcl/Streams,hortonworks/streamline,hortonworks/streamline,hortonworks/streamline,hmcl/Streams,hmcl/Streams,hortonworks/streamline