Changed font weight to look less muddy

Changed the font weight to look a bit less muddy. Any reason why we cant use a number instead of bold?

public/css/less/grafana.less

@@ -317,7 +317,7 @@
     margin: 10px 105px;
     strong {
       color: @headingsColor;
-      font-weight: bold;
+      font-weight: 500;
     }
   }