Change replay button text to be centered

[jmkulwik]

Issue: code-dot-org/dance-party#354

Before:

After:
Chrome/DanceParty

IE/Applab

Mobile/DanceParty

[Hamms]

Interestingly, it looks like we actually override the margins for this element in several of the places we use it. In particular, compare the buttons on https://staging-studio.code.org/s/coursea-2018/stage/4/puzzle/7 with those in /s/dance.

I'd be inclined to do a more surgical change for this, and instead just add text-align: center to the #again-button:not(.arrow-container) { definition here

code-dot-org/apps/style/common.scss

Lines 1372 to 1387 in 1e1c964

	#again-button:not(.arrow-container) {
	background-color: $green;
	border: 1px solid $green;
	color: white;
	margin-left: 0px;
	margin-right: 10px;
	}
	#continue-button:not(.arrow-container), #confirm-button:not(.arrow-container) {
	background-color: $orange;
	border: 1px solid $orange;
	color: white;
	margin-left: 0px;
	margin-right: 10px;
	text-align: center;
	}