update Dockerfile (#97)

Dockerfile

@@ -1,10 +1,19 @@
-FROM golang:1.12-alpine
-
-WORKDIR /etc
-ADD . . 
-RUN apk update && \ 
-    apk add git make clang build-base pkgconfig openssh cmake libssh2 libssh2-dev openssl bash ninja
-RUN go get -u -d -v .
-RUN ./install.sh 
-RUN ./gitql -v
-RUN echo "INSTALLED " $TARGET_OS_ARCH
+# run with:
+# docker build -t gitql .
+# docker run -it --entrypoint /bin/sh gitql:latest
+
+FROM golang:1.15.2-alpine3.12 as builder
+
+WORKDIR /src
+COPY go.mod .
+COPY go.sum .
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -o /bin/gitql
+
+FROM alpine:3.12
+RUN apk add -U git
+COPY --from=builder /bin/gitql /bin/
+
+ENTRYPOINT ["gitql"]