Since my .vimrc already installs the same version of vim plug,
and since any user can symlink my dotfiles, using a PKGBUILD to
install it is redundant and arguably less portable.
Since the community package doesn't include the fish completions found
upstream, we install them here instead. There is already a bug report
about the fish completions, and when it eventually gets fixed, these
steps can be removed from the PKGBUILD.
Bug report: https://bugs.archlinux.org/task/55786
