Allow rebuild on Mac

Not sure why, but spawn changes in Node v0.10.x meant that `rebuild.js`
never exited successfully without passing stdio. (#131, #123)

rebuild.js

@@ -4,5 +4,5 @@ var spawn = require('child_process').spawn;
 // the toolchain exists. This is here to not rebuild on windows, as that
 // had issues as of https://github.com/andrew/node-sass/issues/123
 if (process.platform === 'darwin' || process.platform === 'linux') {
-  spawn('node-gyp', ['rebuild']);
+  spawn('node-gyp', ['rebuild'], {stdio: 'inherit'});
 }