Fix bold style

I'm not sure if this ever worked before but no styles were being applied
to strong tags.

output/assets/css/theme.css

@@ -341,6 +341,10 @@ h1 small {
   margin-top: 8px;
 }
 
+strong {
+  font-weight: bold;
+}
+
 #isso-thread {
   font-size: 80%;
 }

themes/pleasant/static/assets/css/theme.css

@@ -341,6 +341,10 @@ h1 small {
   margin-top: 8px;
 }
 
+strong {
+  font-weight: bold;
+}
+
 #isso-thread {
   font-size: 80%;
 }