Fixed regular expression for TTS.

But sometimes there is a strange error:
sh: -c: line 0: unexpected EOF while looking for matching `''
sh: -c: line 1: syntax error: unexpected end of file
/Users/thyrlian/workspace/ruby/agile_notifier/lib/agile_notifier/tts.rb:67:in `speak_on_osx': No available voice found, please check if you have downloaded voice [Boing] in System Preferences -> Speech (RuntimeError)
	from /Users/thyrlian/workspace/ruby/agile_notifier/lib/agile_notifier/tts.rb:14:in `speak'