[fix] Remove some redundant stuff and add stuff for macos

config/fish/functions/ga.fish

@@ -0,0 +1,13 @@
+function ga --argument-names source target --description "Check how much ahead a git branch is from another"
+    if test -z "$source"
+        echo "Usage: ga source target"
+        return 1
+    end
+    if test -z "$target"
+        set target (git rev-parse --abbrev-ref HEAD)
+    end
+    echo "$source"\t"$target"
+    git rev-list --left-right --count "$source"..."$target"
+end
+
+