fix problem with arguments

Dockerfile

@@ -1,13 +1,21 @@
 FROM debian:wheezy
 MAINTAINER wefork
 
+# Declare Arguments
+ARG NODE_VERSION
+ARG METEOR_RELEASE
+ARG NPM_VERSION
+ARG ARCHITECTURE
+ARG SRC_PATH
+
+# Set the environment variables (defaults where required)
 ENV BUILD_DEPS="wget curl bzip2 build-essential python git ca-certificates"
 ENV GOSU_VERSION=1.10
-ARG NODE_VERSION=v0.10.48
-ARG METEOR_RELEASE=1.3.5.1
-ARG NPM_VERSION=3.10.10
-ARG ARCHITECTURE=linux-x64
-ARG SRC_PATH=./
+ENV NODE_VERSION ${NODE_VERSION:-v0.10.48}
+ENV METEOR_RELEASE ${METEOR_RELEASE:-1.3.5.1}
+ENV NPM_VERSION ${NPM_VERSION:-3.10.10}
+ENV ARCHITECTURE ${ARCHITECTURE:-linux-x64}
+ENV SRC_PATH ${SRC_PATH:-./}
 
 # Copy the app to the image
 COPY ${SRC_PATH} /home/wekan/app