completions/git: Shorten alias descriptions

I have an alias called "lg" for

log --color --graph --pretty=format:\'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset\' --abbrev-commit --first-parent

Having that in my completions ensures that git commands essentially
always use one column at most. That's not great, so we now shorten it
to 35 chars (plus an annoying 2 for ".." because I can't be bothered
to check for unicode support - an argument for a "string ellipsize", I guess?)

share/completions/git.fish

@@ -732,8 +732,9 @@ function __fish_git_aliases
         begin
             set -l name (string replace -r '^.*\.' '' -- $key)
             # Only use the first line of the value as the description.
-            set -l val (printf '%s\n' $value)[1]
-            printf "%s\t%s\n" $name "Alias for $val"
+            # Also shorten it to 35 chars.
+            set -l val (printf '%s\n' $value | string replace -r '^(.{0,35}).+' '$1..')[1]
+            printf "%s\t%s\n" $name "Alias: $val"
         end
     end
 end