Bug fix: :!= symbol and calls to #!= makes the parser send a syntax error message

This is affecting any software relying on dynamically sending the message !=, like puppet < 2.7's augeas provider.

How to reproduce the bug:

ruby -e 'puts 8.!= 5'
ruby -e 'puts :!='

That should print

true
!=

but prints a syntax error message instead.