Fix SASS mixin for input-placeholders.

[leddie24]

See http://www.codechewing.com/library/create-sass-mixin-for-styling-placeholders-css/ for information.

It’s important that each vendor’s style is contained within a separate selector block of their own. If we were to merge the selectors together, then a browser which doesn’t understand one of the selectors will actually invalidate the entire line of selectors.

[msftclas]

Hi @leddie24, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, MSBOT;

[mikewheaton]

Approved

[gokunymbus]

Approved