Update istanbul
Merge pull request #2 from aredridel/update-istanbul

Update istanbul
Convert to asynchronous interface
Appease jshint
Z̨a̻̬̟̣l̗̯̺͎͞g̞̗̜̭̩̗͕o, mindflayer, your day is not this!
Remove assumption about test cwd
Simplify internal state
breaking: Simplify interface to only return error or filename, not a whole descriptive object.
Make tests independent
Integrate locate function into resolve method