worth adding 'bower_components' to default ignore?

[peter-mouland]

is there an occasion when you would want to instrument bower_components? Am i right in thinking these are external dependencies, or do people user bower for other use cases?

I suggest this because i get a timeout with my tests when using this transform within karma without using: istanbul({ ignore: ['**/bower_components/**'] })

[devongovett]

I haven't really used bower, but this sounds reasonable to me. If you make a pull request, I'll merge it.