Update Dockerfile

Add git and OpenSSH to the default Docker image so we can use git over ssh.

Dockerfile

@@ -1,5 +1,8 @@
 FROM node:6-alpine
 
+RUN apk update && apk upgrade && \
+    apk add --no-cache bash git openssh
+
 ENV WIKI_JS_DOCKER 1
 
 RUN mkdir -p /usr/src/app