Strip trailing new lines

StatsD splits its packets on `\n` to get each message, so it interprets the trailing `\n` g2s sends as meaning there's a blank line afterwards. When running StatsD with a console backend, we see an error message (`13 Dec 22:34:34 - DEBUG: Bad line: 1 in msg ""`) for every packet.

This patch fixes this by stripping the final `\n` from each packet as they're being constructed.