Hide number spinner in firefox browsers.

[chetankhilosiya]

I have added the css for hiding the spinner appearing on input type number specific to firefox browser.
Tested in Firefox 57.0 (64-bit).

[googlebot]

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[chetankhilosiya]

I signed the CLA agreement!!!

[googlebot]

CLAs look good, thanks!

[amcdnl]

LGTM

[jelbourn]

LGTM

[chetankhilosiya]

Thanks guys, that was my first ever contribution to this project and Open Source world in general!!!

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