chore(makefile): polish Makefile

Makefile

@@ -1,4 +1,8 @@
-.PHONY: build clean dist
+# --- PREAMBLE
+SHELL := bash
+.ONESHELL:
+.SHELLFLAGS := -eu -o pipefail -c
+MAKEFLAGS += --warn-undefined-variables
 
 BUILD_DATE := $(shell date +'%Y%m%d')
 VERSION := $(shell support/get-version.sh)
@@ -7,18 +11,21 @@ build:
 	go build -o target/gomicsv \
     -ldflags="-X main.buildDate=$(BUILD_DATE) -X main.versionString=$(VERSION)" \
     cmd/gomicsv/main.go
+.PHONY: build
 
 clean:
-	rm -rf target/; \
+	rm -rf target/
+.PHONY: clean
 
 dist: build
-	rm -rf target/dist; \
-	rm -rf target/*.zip; \
-	mkdir -p target/dist/gomicsv; \
-	cp target/gomicsv target/dist/gomicsv/gomicsv; \
-	cp README.md target/dist/gomicsv; \
-	cp COPYING.md target/dist/gomicsv; \
-	cp CHANGELOG.md target/dist/gomicsv; \
-	pushd target/dist; \
-	zip -r ../Gomics-v_$(VERSION).zip gomicsv; \
-	rm -rf gomicsv; \
+	rm -rf target/dist
+	rm -rf target/*.zip
+	mkdir -p target/dist/gomicsv
+	cp target/gomicsv target/dist/gomicsv/gomicsv
+	cp README.md target/dist/gomicsv
+	cp COPYING.md target/dist/gomicsv
+	cp CHANGELOG.md target/dist/gomicsv
+	pushd target/dist
+	zip -r ../Gomics-v_$(VERSION).zip gomicsv
+	rm -rf gomicsv
+.PHONY: dist