Change refs for joyent/libuv repo to libuv/libuv
Change refs for joyent/libuv repo to libuv/libuv

* Replace references from github.com/joyent/libuv to
github.com/libuv/libuv

Similar to https://github.com/neovim/neovim/pull/1562

fwalch/homebrew-neovim,jszakmeister/homebrew-neovim,timfeirg/homebrew-neovim,rf-/homebrew-neovim,thyrgle/homebrew-neovim,mattbailey/homebrew-neovim