update Dockerfile implementation

* fix $GOPATH usage
* improve layer caching

.dockerignore

@@ -0,0 +1,11 @@
+bin/
+cmd/drone-server/drone_bindata.go
+dist/
+doc/
+
+.dockerignore
+.drone.yml
+.gitignore
+Dockerfile
+LICENSE
+README.md

Dockerfile

@@ -1,19 +1,19 @@
-# Docker image for Drone's slack notification plugin
-#
-#     docker build --rm=true -t drone/drone-server .
-
 FROM golang:1.4.2
+
 ENV DRONE_SERVER_PORT :80
-
+WORKDIR $GOPATH/src/github.com/drone/drone
-ADD . /gopath/src/github.com/drone/drone/
-WORKDIR /gopath/src/github.com/drone/drone
-
-RUN apt-get update                                                                       \
-	&& apt-get install -y libsqlite3-dev                                                 \
-	&& git clone git://github.com/gin-gonic/gin.git $GOPATH/src/github.com/gin-gonic/gin \
-	&& go get -u github.com/jteeuwen/go-bindata/...                                      \
-	&& make bindata deps                                                                 \
-	&& make build
 
 EXPOSE 80
-ENTRYPOINT ["/gopath/src/github.com/drone/drone/bin/drone"]
+
+ENTRYPOINT ["/usr/local/bin/drone"]
+
+RUN apt-get update                                                                       \
+    && apt-get install -y libsqlite3-dev                                                 \
+    && git clone git://github.com/gin-gonic/gin.git $GOPATH/src/github.com/gin-gonic/gin \
+    && go get -u github.com/jteeuwen/go-bindata/...
+
+ADD . .
+RUN make bindata deps           \
+    && make build               \
+    && mv bin/* /usr/local/bin/ \
+    && rm -rf bin cmd/drone-server/drone_bindata.go