fix(make): build_docker_image failed (jeessy2#522)

Looks like it fails after jeessy2#498 because it requires buildkit, add `DOCKER_BUILDKIT=1` to enable buildkit to fix this

Also, add `--no-cache` to `apk add` to not cache the index locally, forgot to do that in jeessy2#498.

Dockerfile

@@ -5,7 +5,7 @@ WORKDIR /app
 COPY . .
 ARG TARGETOS TARGETARCH
 
-RUN apk add git make tzdata \
+RUN apk add --no-cache git make tzdata \
     && GOOS=$TARGETOS GOARCH=$TARGETARCH make clean build
 
 # final stage

Makefile

@@ -3,7 +3,8 @@
 VERSION=$(shell git describe --tags `git rev-list --tags --max-count=1`)
 BIN=ddns-go
 DIR_SRC=.
-DOCKER_CMD=docker
+DOCKER_ENV=DOCKER_BUILDKIT=1
+DOCKER=$(DOCKER_ENV) docker
 
 GO_ENV=CGO_ENABLED=0
 GO_FLAGS=-ldflags="-X main.version=$(VERSION) -X 'main.buildTime=`date`' -extldflags -static -s -w" -trimpath
@@ -15,7 +16,7 @@ build: $(DIR_SRC)/main.go
 	@$(GO) build $(GO_FLAGS) -o $(BIN) $(DIR_SRC)
 
 build_docker_image:
-	@$(DOCKER_CMD) build -f ./Dockerfile -t ddns-go:$(VERSION) .
+	@$(DOCKER) build -f ./Dockerfile -t ddns-go:$(VERSION) .
 
 test:
 	@$(GO) test ./...