Set compose version to "2" (#299)

This docker-compose works well as a version-2 file and is available to more installations.

Co-authored-by: Nelson Estevão <nelsonmestevao@gmail.com>

docker-compose.yml

@@ -1,4 +1,4 @@
-version: "3.8"
+version: "2"
 services:
   jekyll:
       image: jekyll/jekyll:3.8
@@ -9,4 +9,4 @@ services:
           - .:/srv/jekyll
       environment:
         JEKYLL_UID: 1001
-        JEKYLL_GID: 1001
+        JEKYLL_GID: 1001