Attempt at fixing docker build /cc @kiloreux

packages/@uppy/companion/.dockerignore

@@ -0,0 +1 @@
+node_modules

packages/@uppy/companion/Dockerfile

@@ -1,21 +1,21 @@
-FROM alpine:3.6
-
-RUN apk add --update nodejs \
-	           nodejs-npm 
+FROM node:8.11.4-alpine
 
 COPY package.json /app/package.json
 
 WORKDIR /app
 
-RUN apk --update add  --virtual native-dep \
+# Install node_modules
+# * to optionally copy lock files that _might_ _not_ exist
+ADD package.json package-*.json yarn.* /tmp/
+RUN cd /tmp && apk --update add  --virtual native-dep \
   make gcc g++ python libgcc libstdc++ && \
   npm  install && \
   apk del native-dep
+RUN mkdir -p /app && cd /app && ln -nfs /tmp/node_modules
 RUN apk add bash
 COPY . /app
 ENV PATH "${PATH}:/app/node_modules/.bin"
 RUN npm run build
 CMD ["node","/app/lib/standalone/start-server.js"]
-# This can be overwritten later
-EXPOSE 3020
-
+# This can be overruled later
+EXPOSE 3020