Add GitLab support (#658)

Close #658.

README.md

@@ -29,6 +29,8 @@ Install plugins using the `install` command followed by the path to the reposito
 fisher install jorgebucaran/nvm.fish
 ```
 
+> To install a plugin from GitLab, prefix the repository with `gitlab.com/`.
+
 To get a specific version of a plugin add an `@` symbol after the plugin name followed by a tag, branch, or [commit](https://git-scm.com/docs/gitglossary#Documentation/gitglossary.txt-aiddefcommit-ishacommit-ishalsocommittish).
 
 ```console

functions/fisher.fish

@@ -91,6 +91,12 @@ function fisher --argument-names cmd --description "A plugin manager for Fish"
                         set url https://api.github.com/repos/\$name[1]/tarball/\$name[2]
                         set header 'Accept: application/vnd.github.v3+json'
 
+                        if string match -q 'gitlab.com/*' \$name[1]
+                            set bare (string replace 'gitlab.com/' '' \$name[1])
+                            set repo (string split '/' \$bare)
+                            set url https://gitlab.com/{\$bare}/-/archive/{\$name[2]}/{\$repo[2]}-{\$name[2]}.tar.gz
+                        end
+
                         echo Fetching (set_color --underline)\$url(set_color normal)
 
                         if curl --silent -L -H \$header \$url | tar -xzC \$temp -f - 2>/dev/null