Add ca-certificates to the docker image

This is to ensure that the bot can connect to homeservers behind ssl.

Signed-off-by: Travis Ralston <travpc@gmail.com>

Dockerfile

@@ -15,6 +15,7 @@ FROM alpine:3.6
 ENV BIND_ADDRESS=:4050 DATABASE_TYPE=sqlite3 DATABASE_URL=/data/go-neb.db?_busy_timeout=5000
 
 COPY --from=builder /tmp/go-neb/bin/go-neb /go-neb
+RUN apk add --no-cache ca-certificates
 
 VOLUME /data
 EXPOSE 4050