Fix Docker files

docker/Dockerfile

@@ -1,10 +1,9 @@
-FROM golang:alpine3.6
+FROM docker.io/golang:1.12.5-alpine3.9
 
 RUN mkdir /build
 
 WORKDIR /build
 
-RUN apk --update --no-cache add openssl bash git && \
-    go get github.com/constabulary/gb/...
+RUN apk --update --no-cache add openssl bash git
 
 CMD ["bash", "docker/build.sh"]

docker/build.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-gb build
+./build.sh
 
 # Generate the keys if they don't already exist.
 if [ ! -f server.key ] || [ ! -f server.crt ] || [ ! -f matrix_key.pem ]; then

docker/docker-compose.yml

@@ -7,7 +7,6 @@ services:
     build: ./
     volumes:
       - ..:/build
-      - ./build/pkg:/build/pkg
       - ./build/bin:/build/bin
     networks:
       - internal