Fix typo (#4815)

Author: jkshapiro

mediaqueries-4/Overview.bs

@@ -454,7 +454,7 @@ Media Features</h3>
 			(omitting the colon and value)
 			to evaluate the feature in a <a>boolean context</a>.
 			This is a convenient shorthand for features that have a reasonable value representing 0 or “none”.
-			For example, ''(color)'' is true is the '@media/color' <a>media feature</a> is non-zero.
+			For example, ''(color)'' is true if the '@media/color' <a>media feature</a> is non-zero.
 
 		<li>
 			<a>Media features</a> with “range” type can be written in a <a>range context</a>,