add empty drone.toml to satisfy drone startup requirements

Dockerfile

@@ -6,12 +6,15 @@ WORKDIR $GOPATH/src/github.com/drone/drone
 EXPOSE 80
 
 ENTRYPOINT ["/usr/local/bin/drone"]
+CMD ["-config", "/tmp/drone.toml"]
 
 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/...
 
+RUN touch /tmp/drone.toml
+
 ADD . .
 RUN make bindata deps           \
     && make build               \