Convert Dockerfile to be a mutlistage build

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

Dockerfile

@@ -1,19 +1,20 @@
-FROM alpine:3.6
-
-ENV BIND_ADDRESS=:4050 DATABASE_TYPE=sqlite3 DATABASE_URL=/data/go-neb.db?_busy_timeout=5000
+# Build go-neb
+FROM golang:1.8-alpine as builder
 
 COPY . /tmp/go-neb
 WORKDIR /tmp/go-neb
-ENV GOPATH=/tmp/go-neb/vendor/src:/tmp/go-neb/vendor:/tmp/go-neb
 RUN apk add --no-cache -t build-deps git gcc musl-dev go \
     && go get -u github.com/constabulary/gb/... \
-    && export PATH="/tmp/go-neb/vendor/src/bin:${PATH}" \
     && gb vendor restore \
-    && gb build -f github.com/matrix-org/go-neb \
-    && mv bin/go-neb /go-neb \
-    && cd / \
-    && rm -rf /tmp/* \
-    && apk del build-deps
+    && gb build -f github.com/matrix-org/go-neb
+
+
+# Run go-neb
+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
 
 VOLUME /data
 EXPOSE 4050