Only run rails 4 tests a single time from the command line

I don't know why sprockets wants to concatonate all files in rails 4
but this will explicitly write an empty file for jasmine-specs.js
which stops the duplicate test runs.

This is extremely hackish, but I can't find a way around this.
Merge pull request #83 from zmoazeni/rails-4-single-test-run

Only run rails 4 tests a single time from the command line