Add GitLab support.

Add the possibility to add plugins from gitlab. Resolves #657.

README.md

@@ -31,6 +31,12 @@ Install plugins using the `install` command followed by the path to the reposito
 fisher install ilancosman/tide
 ```
 
+To install a plugin from GitLab, prefix `gitlab.com/`.
+
+```console
+fisher install gitlab.com/ainmosni/fish-aws
+```
+
 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

@@ -84,6 +84,12 @@ function fisher --argument-names cmd --description "A plugin manager for Fish"
                         set name (string split \@ $plugin) || set name[2] HEAD
                         set url https://codeload.github.com/\$name[1]/tar.gz/\$name[2]
 
+                        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[1]}-{\$name[2]}.tar.gz
+                        end
+
                         echo Fetching (set_color --underline)\$url(set_color normal)
 
                         if curl --silent \$url | tar --extract --gzip --directory \$temp --file - 2>/dev/null