eventids2.c: reduce size

* ext/ripper/eventids2.c (token_assoc): reduce size.  unsigned
  short can hold 65535 at least.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48169 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-28

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48170 b2dd03c8-39d4-4d8f-98ff-823fe69b080e