Don't trust import builtins to check for python3
Don't trust import builtins to check for python3

Fixes #24

ymero/line_profiler,Doctorhoenikker/line_profiler,amegianeg/line_profiler,Doctorhoenikker/line_profiler,ymero/line_profiler,eblur/line_profiler,amegianeg/line_profiler,eblur/line_profiler