unify makefile syntax (#177)

Author: xoxys

Makefile

@@ -74,7 +74,7 @@ test:
 build: $(DIST)/$(EXECUTABLE)
 
 $(DIST)/$(EXECUTABLE): $(SOURCES)
-	GOOS=${TARGETOS} GOARCH=${TARGETARCH} GOARM=$(GOARM) $(GO) build -v -tags '$(TAGS)' -ldflags '-extldflags "-static" $(LDFLAGS)' -o $@ ./cmd/$(EXECUTABLE)
+	GOOS=$(TARGETOS) GOARCH=$(TARGETARCH) GOARM=$(GOARM) $(GO) build -v -tags '$(TAGS)' -ldflags '-extldflags "-static" $(LDFLAGS)' -o $@ ./cmd/$(EXECUTABLE)
 
 $(DIST_DIRS):
 	mkdir -p $(DIST_DIRS)