Fixes incorrect supportDirectory for Safari

When we look for "WebKit" in the userAgent string, Safari passes even though it does not support directory uploads. 

Since only Chrome supports directory upload right now, let's just test for Chrome instead.

Author: dshefchik

src/flow.js

@@ -57,7 +57,7 @@
      * Check if directory upload is supported
      * @type {boolean}
      */
-    this.supportDirectory = /WebKit/.test(window.navigator.userAgent);
+    this.supportDirectory = /Chrome/.test(window.navigator.userAgent);
 
     /**
      * List of FlowFile objects