fix(modal): missing require in modal

- Fix incorrect require of css instead of position module

Closes #5786

Author: mhchen

src/modal/index.js

@@ -1,8 +1,8 @@
+require('../position');
 require('../stackedMap');
 require('../../template/modal/backdrop.html.js');
 require('../../template/modal/window.html.js');
 require('./modal');
-require('../position/position.css');
 
 var MODULE_NAME = 'ui.bootstrap.module.modal';