fisher: mv: target ~/.cache/fisher/github.com/... is not a directory

I cannot seem to be able to install new packages using any 3.2.x version of fisher.

Here is an example using 3.2.0, but the same error occurs with any later version including master:

▶ curl -sSo ~/.config/fish/functions/fisher.fish https://raw.githubusercontent.com/jorgebucaran/fisher/3.2.0/fisher.fish
▶ source ~/.config/fish/functions/fisher.fish
▶ rm -r ~/.config/fisher/ ~/.cache/fisher/ ~/.config/fish/fishfile
▶ fisher add reitzig/sdkman-for-fish@v1.3.0
created empty fishfile in ~/.config/fish/fishfile
fetching https://codeload.github.com/reitzig/sdkman-for-fish/tar.gz/v1.3.0
mv: target '/home/tobia/.cache/fisher/github.com/reitzig/sdkman-for-fish' is not a directory
cp: cannot stat '/home/tobia/.cache/fisher/github.com/reitzig/sdkman-for-fish': No such file or directory
done in 0.50s

Here is the same command with 3.1.1, which works properly:

▶ curl -sSo ~/.config/fish/functions/fisher.fish https://raw.githubusercontent.com/jorgebucaran/fisher/3.1.1/fisher.fish
▶ source ~/.config/fish/functions/fisher.fish
▶ rm -r ~/.config/fisher/ ~/.cache/fisher/ ~/.config/fish/fishfile
▶ fisher add reitzig/sdkman-for-fish@v1.3.0
created empty fishfile in ~/.config/fish/fishfile
fetching https://codeload.github.com/reitzig/sdkman-for-fish/tar.gz/v1.3.0
linking ~/.config/fish/functions/sdk.fish
linking ~/.config/fish/completions/sdk.fish
linking ~/.config/fish/conf.d/sdk.fish
added 1 package in 0.61s

I’m using fish 2.7.1, installed from the default apt repository of Ubuntu 18.04