Pull margin of auth tab content up under tabs

Fix the border poking out under the active tab.

h/css/common.scss

@@ -526,7 +526,7 @@ blockquote {
   background: $white;
   border: solid 1px $grayLighter;
   line-height: 1.4;
-  margin-top: -2px;
+  margin-top: -3px;
   padding: 16px;
   position: relative;