Merge when updating submodules on make

When  running make, the submodule update will remove all local changes.
Adding flag --rebase or --merge does solve the issue. rebase will
probably make it cleaner, but it might stop on conflict, thus --merge
will result in fewer (probably none).

Makefile

@@ -49,7 +49,7 @@ ${DIST_DIR}:
 	@@mkdir -p ${DIST_DIR}
 
 init:
-	@@if [ -d .git ]; then git submodule update --init --recursive; fi
+	@@if [ -d .git ]; then git submodule update --init --recursive --merge; fi
 
 jquery: init ${JQ}
 jq: init ${JQ}