Set @echo off in ceylon-format.bat script

This should fix a problem @sgalles found, where `ceylon help` would
print a huge amount of info about ceylon-formatter; see this gist:
https://gist.github.com/sgalles/df91331181c742a18e8c

Thanks @Quintesse for helping me figure it out.

(Sorry @echo for pinging you btw.)