Fix node-webkit version finding in build_native_modules.py
Fix node-webkit version finding in build_native_modules.py

- Update the regular expression used to find the node-webkit version from
README.md.

FIX rogerwang/node-webkit#2842

nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js