fix: Docker fixes

Dockerfile

@@ -1,13 +1,12 @@
-FROM node:6-alpine
+FROM node:8-alpine
 
 RUN apk update && apk upgrade && \
     apk add --no-cache bash git openssh
 
 ENV WIKI_JS_DOCKER 1
 
-RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app
 RUN npm install wiki.js@latest
 
 EXPOSE 3000
-CMD [ "node", "server" ]
+ENTRYPOINT [ "node", "server" ]