Use the alpine image

Dockerfile

-FROM golang:1.7
+FROM golang:1.7-alpine
 
 ADD . /go/src/github.com/nsheridan/cashier
+RUN apk add --update build-base
 RUN go install github.com/nsheridan/cashier/cmd/cashierd
 
-ONBUILD COPY . /cashier
 WORKDIR /cashier
 ENTRYPOINT /go/bin/cashierd