reduce fonts size for wiki render

app/assets/stylesheets/gitlab_bootstrap/typography.scss

@@ -88,13 +88,14 @@ a:focus {
  */
 .wiki {
   font-size: 13px;
+  line-height: 20px;
 
   code { padding: 0 4px; }
   p { font-size: 13px; }
-  h1 { font-size: 32px; line-height: 40px; margin: 10px 0;}
-  h2 { font-size: 26px; line-height: 40px; margin: 10px 0;}
-  h3 { font-size: 22px; line-height: 40px; margin: 10px 0;}
-  h4 { font-size: 18px; line-height: 20px; margin: 10px 0;}
+  h1 { font-size: 26px; line-height: 40px; margin: 10px 0;}
+  h2 { font-size: 22px; line-height: 40px; margin: 10px 0;}
+  h3 { font-size: 18px; line-height: 40px; margin: 10px 0;}
+  h4 { font-size: 16px; line-height: 20px; margin: 10px 0;}
   h5 { font-size: 14px; line-height: 20px; margin: 10px 0;}
   h6 { font-size: 12px; line-height: 20px; margin: 10px 0;}
   .white .highlight pre { background: #f5f5f5; }