Update tasks/usemin.js

Line 152
Change: I removed [0] from the filepath response.
Rationale: I am running multiple builds for different locales in a loop, restricting the filepath response results in the 1st file rev'd in the loop persisting and being copied to all corresponding index.html's.
Notes: Please can you let me know if this will cause any damage, or whether there is an existing way to achieve the goal.