core: check for gh-release
Stop when this can't be found early on.
Fixes
#
# Docker push should happen after you make the new release and uploaded it to Github.
+ifeq (, $(shell which gh-release))
+ $(error "No gh-release in $$PATH, install with `go get progrium/gh-release`")
+endif
+
NAME:=coredns
VERSION:=$(shell grep 'coreVersion' coremain/version.go | awk '{ print $$3 }' | tr -d '"')
ARCH:=$(shell uname -m)
