Pressing Enter doesn't work

Thank you for the great plugin. Everything works as expected! The only issue is pressing Enter wouldn’t trigger submit. Pressing Enter move the focus to the search box and then it needs one more time to press the Enter. Is there any easy fix to make the enter submits the search instead of pointing mouse on the magnifier icon or pressing enter twice?

I have users complaining that search doesn’t work when they simply type search query and press enter at the end.

http://ww.wp.xz.cn/extend/plugins/wd-search-form/