use simple regexp pattern according to RFC3986 Appendix B

This commit was done at open-browser.vim repository at first.
https://github.com/tyru/open-browser.vim/commit/93c7c5da746d1caf435e908a196dfe3c232bfffe
don't escape each path

This commit was done at open-browser.vim repository at first.
https://github.com/tyru/open-browser.vim/commit/fa5fca43351da8b76416cf4528af5f6dd11ded9f