Added update to assure graying corpus statistic by deleting the first line in vc builder(plus test)

Change-Id: Id44736f134c00e1a1be002bf14e00e6efa26ad02
(cherry picked from commit 4c4c3eb9de42c3c61547b475bd0b48ae509c2c67)
diff --git a/dev/js/src/vc.js b/dev/js/src/vc.js
index 0431f92..af09132 100644
--- a/dev/js/src/vc.js
+++ b/dev/js/src/vc.js
@@ -242,13 +242,15 @@
 
     
     /**
-     * Clean the virtual document to uspecified doc.
+     * Clean the virtual document to unspecified doc.
      */
     clean : function() {
       if (this._root.ldType() !== "non") {
         this._root.destroy();
         this.root(unspecDocClass.create(this));
       };
+      //update for graying corpus statistic by deleting the first line of the vc builder
+      this.update();
       return this;
     },