Fix typo

Author: GuillaumeGomez

src/librustdoc/html/static/rustdoc.css

@@ -1343,7 +1343,7 @@ h4 > .notable-traits {
 @media (min-width: 701px) {
 	/* In case there is no documentation before a code block, we need to add some margin at the top
 	to prevent an overlay between the "collapse toggle" and the information tooltip.
-	However, it's needed needed with smaller screen width because the doc/code block is always put
+	However, it's not needed with smaller screen width because the doc/code block is always put
 	"one line" below. */
 	.information:first-child > .tooltip {
 		margin-top: 16px;