Apply correct font-weight to strong tags in alerts

(cherry picked from commit 6116b0a6)

aleksis/core/static/style.scss

@@ -513,6 +513,10 @@ th.orderable.desc > a {
   margin: 0;
 }
 
+.alert strong {
+  font-weight: 700;
+}
+
 .alert > p, .alert > div {
   margin: 10px;
   padding: 10px;