🐳 Improve automatic docker build

docker/images/n8n/Dockerfile

@@ -1,5 +1,9 @@
 FROM mhart/alpine-node:10
 
+ARG N8N_VERSION
+
+RUN if [ -z "$N8N_VERSION" ] ; then echo "The N8N_VERSION argument is missing!" ; exit 1; fi
+
 # Update everything and install needed dependencies
 RUN apk add --update \
 	graphicsmagick
@@ -10,7 +14,7 @@ USER root
 # Install n8n and the also temporary all the packages
 # it needs to build it correctly.
 RUN apk --update add --virtual build-dependencies python build-base && \
-	npm_config_user=root npm install -g n8n && \
+	npm_config_user=root npm install -g n8n@${N8N_VERSION} && \
 	apk del build-dependencies
 
 WORKDIR /data

docker/images/n8n/hooks/build

@@ -0,0 +1,2 @@
+#!/bin/bash
+docker build --build-arg N8N_VERSION=$DOCKER_TAG -f $DOCKERFILE_PATH -t $IMAGE_NAME .