Fix some references to non-existant polyfill directory.

Looks like the name of the directory is "poly" rather than "polyfill".

BUG=None
TEST=None
R=humper@google.com, jcgregorio@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/610003003

experimental/webtry/README.md

@@ -91,5 +91,4 @@ Third Party Code
 ----------------
 
   * res/js/polyfill.js - Various JS polyfill libraries. To rebuild or update
-    see polyfill/README.md.
-
+    see poly/README.md.

experimental/webtry/poly/README.md

@@ -3,16 +3,15 @@ polyfill.js
 
 To rebuild or update res/js/polyfill.js you will need to have
 [node.js](http://nodejs.org/) installed. Once you have it installed run the
-following:
+following (assuming you are in experimental/webtry directory):
 
-    cd polyfill
-    npm install
-    grunt
+$ cd poly
+$ npm install
+$ grunt
 
 If you want to create a verion of the polyfill.js that hasn't been minified,
 say for debugging purposes, then run:
 
-
-    cd polyfill
-    npm install
-    grunt notmin
+$ cd poly
+$ npm install
+$ grunt notmin