fixed character-set detection regex

Previous regex matched COLLATE value instead of CHARACTER SET. For
example:

> CREATE DATABASE `test` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */

Returned utf8_bin instead of utf8 causing an unfortunate database refresh in my
configuration. Fixed the regex by adding the optional presence of the COLLATE
keyword.
Merge pull request #133 from obilodeau/master

fixed character-set detection regex