Fix tooltip text display

Author: GuillaumeGomez

src/librustdoc/html/static/rustdoc.css

@@ -1098,6 +1098,10 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 	border-style: solid;
 }
 
+.tooltip:hover .tooltiptext {
+	display: inline;
+}
+
 .tooltip.compile_fail, .tooltip.should_panic, .tooltip.ignore {
 	font-weight: bold;
 	font-size: 20px;