Update lib/phantomjs/version.rb

Updated to version 1.8 of phantomjs
Update lib/phantomjs/platform.rb

Bump version to 1.8.1
Update lib/phantomjs/version.rb

bump version to 1.8.1.0
Fixed local install check for phantomjs
Fixed logic for trying to execute phantomjs version

Simply just ignore the exception here
Merge pull request #8 from jeffborg/master

Updated phantomjs to 1.8.1