[css-2017] Spell check.

Author: dbaron

css-2017/Overview.bs

@@ -108,7 +108,7 @@ Background: The W3C Process and CSS</h3>
 
 		<dt>Recommendation (REC)
 		<dd>
-			This is the completed state of a W3C spec and represents a maintainance phase.
+			This is the completed state of a W3C spec and represents a maintenance phase.
 			At this point the WG only maintains an errata document
 			and occasionally publishes an updated edition that incorporates the errata back into the spec.
 	</dl>