Set correct version on static-build

Right now, we are compiling into a container. Doing this Makefile.main
is not getting correct VERSION env var because we dont have TRAVIS_TAG
in the container.

To avoid this problem, we are setting always our VERSION when make
static-build is called.

Signed-off-by: Antonio Navarro Perez <[email protected]>

Author: ajnavarro

Makefile

@@ -31,7 +31,7 @@ static-package:
 	docker rm gitbase-temp
 
 # target used in the Dockerfile to build the static binary
-static-build: VERSION ?= $(shell git describe --exact-match --tags 2>/dev/null || "dev-$(git rev-parse --short HEAD)$(test -n "`git status --porcelain`" && echo "-dirty" || true)")
+static-build: VERSION = $(shell git describe --exact-match --tags 2>/dev/null || "dev-$(git rev-parse --short HEAD)$(test -n "`git status --porcelain`" && echo "-dirty" || true)")
 static-build: LD_FLAGS += -linkmode external -extldflags '-static -lz' -s -w
 static-build: GO_BUILD_PATH ?= github.com/src-d/gitbase/...
 static-build: