Fix whitespace issue in _Gruntfile template

Here is what I got when using `grunt deploy`: 

Running "coffeelint:all" (coffeelint) task

Gruntfile.coffee
  ✖  line 94   Line contains inconsistent indentation  Expected 4 got 5
  ✖  line 95   Line contains inconsistent indentation  Expected 4 got 3
  ✖  line 100  Line contains inconsistent indentation  Expected 4 got 8

✖ 3 errors

Warning: Task "coffeelint:all" failed. Use --force to continue.