[lint addon] Wrap long lint messages

e.g. errors on css `input.someLongClassName {}`

addon/lint/lint.css

@@ -14,6 +14,7 @@
   padding: 2px 5px;
   position: fixed;
   white-space: pre;
+  white-space: pre-wrap;
   z-index: 100;
   max-width: 600px;
   opacity: 0;