Add ability to override using $EDITOR

aliases/available/git.aliases.bash

@@ -28,7 +28,8 @@ alias gdel='git branch -D'
 alias gmu='git fetch origin -v; git fetch upstream -v; git merge upstream/master'
 alias gll='git log --graph --pretty=oneline --abbrev-commit'
 
-case $OSTYPE in
+if [ -z "$EDITOR" ]; then
+    case $OSTYPE in
       linux*)
         alias gd='git diff | vim -R -'
         ;;
@@ -38,4 +39,7 @@ case $OSTYPE in
       *)
         alias gd='git diff'
         ;;
-esac
+    esac
+else
+    alias gd="git diff | $EDITOR"
+fi