Fix docker build

Dockerfile

@@ -1,8 +1,10 @@
-FROM golang
-COPY . /go/src/github.com/raviqqe/liche
-RUN CGO_ENABLED=0 GOOS=linux go get /go/src/github.com/raviqqe/liche
+FROM golang:1.12
+COPY . /src
+ENV CGO_ENABLED=0 GO111MODULE=on GOOS=linux
+WORKDIR /src
+RUN go build -o liche
 
 FROM alpine
 RUN apk --no-cache add ca-certificates
-COPY --from=0 /go/bin/liche /liche
+COPY --from=0 /src/liche /liche
 ENTRYPOINT ["/liche"]