fix yiistrap.less Bs3

<pre>
diff --git a/assets/less/yiistrap.less b/assets/less/yiistrap.less
index 0e6674f..44cbc5a 100644
--- a/assets/less/yiistrap.less
+++ b/assets/less/yiistrap.less
@@ -77,7 +77,7 @@
   }

   .summary {
-    color: @grayLight;
+    color: @gray-light;
     font-size: 12px;
     padding: 6px 0;
     text-align: right;
</pre>