Merge branch 'travis/fix-docker' of https://github.com/t2bot/matrix-appservice-discord into develop

Dockerfile

 FROM node:alpine AS BUILD
 COPY . /tmp/src
 # install some dependencies needed for the build process
-RUN apk add --no-cache -t build-deps make gcc g++ python ca-certificates libc-dev wget
+RUN apk add --no-cache -t build-deps make gcc g++ python ca-certificates libc-dev wget git
 RUN cd /tmp/src \
     && npm install \
     && npm run build