[css-flexbox] bikeshed update

--HG--
extra : rebase_source : 4cede02af4e2c7be1f83224a6cbb65a3749aa1a5

Author: tabatkins

css-flexbox/Overview.bs

@@ -1514,7 +1514,7 @@ The 'flex-basis' property</h4>
 	Applies to: <a>flex items</a>
 	Inherited: no
 	Computed value: as specified, with lengths made absolute
-	Percentages: realtive to the <a>flex container's</a> inner <i>main size</i>
+	Percentages: relative to the <a>flex container's</a> inner <i>main size</i>
 	Media: visual
 	Animatable: as 'width'
 	</pre>