Apparently this works around issue #94 for some people. Thanks to Consus
for the workaround.

Proper installation of shell completions

See merge request pwmt/zathura!25

fish completions should never be installed to share/fish/completions/ as
that directory is reserved exclusively for completions shipped as part
of the fish source code.

Use the same vendor_completions.d/ directory which the default fish
configuration uses.

Both shells provide pkg-config files which declare their designated
completionsdir. Use this as the primary source of truth.

Version 0.4.5