Update Dockerfile

- Update base image to 8.6-alpine
- Quiet npm install output
- Gather advisories after npm install

Dockerfile

@@ -1,20 +1,20 @@
-FROM node:7.10-alpine
+FROM node:8.6-alpine
 
 WORKDIR /usr/src/app
 
 COPY package.json ./
 
-RUN apk --update add curl && \
-    npm install -g npm && \
-    npm install && \
-    /usr/src/app/bin/nsp gather
+RUN npm install --global --quiet npm && \
+    npm install --quiet
 
 RUN adduser -u 9000 -D app
 COPY . ./
 RUN chown -R app:app ./
 
 USER app
 
+RUN ./bin/nsp gather
+
 VOLUME /code
 WORKDIR /code