prefix git with shell

makefile

 MAKEFLAGS += -r
 HASH := $(shell git rev-list -n 1 --abbrev-commit HEAD)
-COMMIT := $(git rev-parse --short HEAD)
+COMMIT := $(shell git rev-parse --short HEAD)
 uname := $(shell uname -s)
 arch := $(shell uname -m)
 TWEEGO := $(shell command -v tweego || echo "$$?")