Do not center align h2s in footer

In Id9b0e955d6e2a113f91484c7ee6bbc9275e3a2ec the css selector
was weakened and started impacting the footer as well.

This restores the old behaviour.

Bug: T180375
Change-Id: Ibfff6e249a3249ae2ee97d31fd50d2f5272a25ae

skinStyles/mobile.special.styles/minerva.less

@@ -21,6 +21,12 @@
 	h2 {
 		// Important given we have no idea which rules special pages are enforcing
 		font-family: @fontFamily !important;
-		text-align: center;
+	}
+
+	.content-header {
+		h1,
+		h2 {
+			text-align: center;
+		}
 	}
 }