ErrorHandler: Renaming \Exception to \Throwable because PHP 7 throws Errors to

[vcampitelli]

At Peekmo\AtomAutocompletePhp\ErrorHandler there's a method called onException that was expecting a \Exception object to display the message and die.

Since PHP 7, errors are thrown too, but as an \Error class. Both \Exception and \Error classes implement a \Throwable interface. To make the code more compliant and avoid Fatal Errors due to an unexpected type received, I'm renaming \Exception to \Throwable in that method.