chore(docs-app): improve deprecation box layout

Deprecated boxes for APIs appear right under the header and were missing
a bit of margin. Boxes for methods still look good even with the
additional margin.

docs/app/assets/css/docs.css

@@ -662,6 +662,10 @@ ul.events > li {
   max-width: 100%;
 }
 
+.deprecation {
+  margin-top: 15px;
+}
+
 .deprecation .title {
   float: left;
   margin-right: 5px;