[css-overflow] Fix typo

Author: frivoal

css-overflow-4/Overview.bs

@@ -1126,10 +1126,10 @@ Fragmentation of Overflow: the 'continue' property</h3>
 	when the [=computed value=] of the 'continue' property is ''discard''
 	and the [=computed value=] of the '-webkit-box-orient' property is ''vertical'':
 	* If the [=specified value=] of the 'display' property is ''-webkit-box'',
-		the [=computed value=] is becomes ''flow-root'' and
+		the [=computed value=] becomes ''flow-root'' and
 		the box establishes a [=BFC=].
 	* If the [=specified value=] of the 'display property is ''-webkit-inline-box'',
-		the [=computed value=] is becomes ''inline-block'' and
+		the [=computed value=] becomes ''inline-block'' and
 		the box establishes a [=BFC=].
 
 	Note: This means that 'line-clamp' will work