Fix Dockerfile

Dockerfile

@@ -3,8 +3,8 @@ FROM node:4 AS frontend-builder
 WORKDIR /home/kape/app
 COPY . .
 ARG NPM_PROXY=""
-RUN test -n ${NPM_PROXY} && npm config set https-proxy ${NPM_PROXY} \
-    || npm install \
+RUN npm config set https-proxy ${NPM_PROXY} \
+    && npm install \
     && npm run build-production
 
 FROM python:2-jessie AS app