Remove reference to acorn

The README.md still referenced acorn.js.

README.md

@@ -3,7 +3,7 @@
 [![Build Status](https://travis-ci.org/Automattic/xgettext-js.svg)](https://travis-ci.org/Automattic/xgettext-js)
 [![NPM version](https://badge.fury.io/js/xgettext-js.svg)](http://badge.fury.io/js/xgettext-js)
 
-xgettext-js is a utility for extracting translatable strings, written in and capable of parsing JavaScript files. It is similar to the [GNU xgettext](http://www.gnu.org/savannah-checkouts/gnu/gettext/manual/html_node/xgettext-Invocation.html) program, but returns strings as a JavaScript array. It makes use of [acorn.js](http://marijnhaverbeke.nl/acorn/) to parse JavaScript code, which facilitates the use of custom logic for string extraction. Because of this, xgettext-js is quite flexible, allowing you to define your own logic for extracting strings from any number of function keywords.
+xgettext-js is a utility for extracting translatable strings, written in and capable of parsing JavaScript files. It is similar to the [GNU xgettext](http://www.gnu.org/savannah-checkouts/gnu/gettext/manual/html_node/xgettext-Invocation.html) program, but returns strings as a JavaScript array. It makes use of [babylon](http://github.com/babel/babylon/) and [estree-walker](https://github.com/Rich-Harris/estree-walker) to parse JavaScript code, which facilitates the use of custom logic for string extraction. Because of this, xgettext-js is quite flexible, allowing you to define your own logic for extracting strings from any number of function keywords.
 
 ## Installation