Replace hardcoded "make" with $(MAKE)

Some systems don't use GNU make by default, and use something like
gnumake or gmake. Respect that when determining the make version.

Author: dankm

Makefile

@@ -27,7 +27,7 @@ GOFMT ?= gofmt -s
 GOFLAGS := -v
 EXTRA_GOFLAGS ?=
 
-MAKE_VERSION := $(shell make -v | head -n 1)
+MAKE_VERSION := $(shell $(MAKE) -v | head -n 1)
 
 ifneq ($(DRONE_TAG),)
 	VERSION ?= $(subst v,,$(DRONE_TAG))