update Dockerfile

Author: wzshiming

dockerfiles/Dockerfile renamed to Dockerfile

@@ -1,6 +1,7 @@
 FROM golang:1.10-alpine3.7 AS builder
-RUN apk add -U git
-RUN go get -u -v github.com/wzshiming/pic2ascii/cmd/pic2ascii
+WORKDIR /go/src/github.com/wzshiming/pic2ascii/
+COPY . .
+RUN go install ./cmd/...
 
 FROM alpine:3.7
 COPY --from=builder /go/bin/pic2ascii /usr/local/bin/