drone: use DRONE_TAG for VERSION if present

The way drone checks out, tags are not available for `git describe`.

Additionally, set GO111MODULE=off in Dapper.

Dockerfile

@@ -35,9 +35,11 @@ VOLUME /var/log
 
 # Dapper/Drone/CI environment
 FROM build AS dapper
+ARG GO111MODULE=off
 ARG GOBIN=/opt/k3c/bin
 ARG GOPATH=/go
-ENV GOBIN=${GOBIN} \
+ENV GO111MODULE=${GO111MODULE} \
+    GOBIN=${GOBIN} \
     GOPATH=${GOPATH}
 ENV DAPPER_ENV REPO TAG DRONE_TAG
 ENV DAPPER_OUTPUT ./bin ./dist

Makefile

@@ -44,9 +44,13 @@ ifndef GOBIN
 	GOBIN := bin
 endif
 
-VERSION=$(shell git describe --match 'v[0-9]*' --dirty='.dirty' --always --tags)
-REVISION=$(shell git rev-parse HEAD)$(shell if ! git diff --no-ext-diff --quiet --exit-code; then echo .dirty; fi)
-RELEASE=${PROG}-$(VERSION).${GOOS}-${GOARCH}
+ifdef DRONE_TAG
+	VERSION = ${DRONE_TAG}
+else
+	VERSION = $(shell git describe --match 'v[0-9]*' --dirty='.dirty' --always --tags)
+endif
+REVISION = $(shell git rev-parse HEAD)$(shell if ! git diff --no-ext-diff --quiet --exit-code; then echo .dirty; fi)
+RELEASE = ${PROG}-${GOOS}-${GOARCH}
 ifndef TAG
 	TAG := $(shell echo "$(VERSION)" | tr '+' '-')-${GOARCH}
 endif