hotfix: Correct dts header

[ValentinTrinque]

Removal of a double definition of Definitions by: in the Gruntfile.js because it's not supported by DefinitelyTyped.

An error is raised when executing npm test (aiming to verify the correctness of the dts file) on the DefinitelyTyped repository.

[cbowdon]

Do they not allow you to do a single line with comma-separated authors?

[ValentinTrinque]

Just FYI, this is the error when I ran npm test :

----------------- For file:tsmonad/tsmonad.d.ts

expected '// Definitions: ' at line 4, column 1:

// Type definitions for TsMonad
// Project: https://github.com/cbowdon/TsMonad
// Definitions by: Chris Bowdon <https://github.com/cbowdon>
// , Valentin Trinque <https://github.com/ValentinTrinque>
^
// Definitions: https://github.com/borisyankov/DefinitelyTyped

However, when I do a single line with comma separation, it works but it creates an over-80-column line. DefinitelyTyped does not talk about column restriction in their guide so I guess it's ok.

[cbowdon]

Would you like to add your name to the header on a single comma-separated line? You've put in some good work so it'd be nice to have you on there. If you're not bothered I'll just merge this as-is.

[ValentinTrinque]

Having my name or not really doesn't matter to me. But I really appreciate your care. You can merge =)