There is an open bug that should be resolved before or during the
Arch Linux Bug Day coming up next month (January 2019). Either way,
manually updating the httpie version becomes impractical after some
time; it's best to apply this fix upstream instead.
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
