chore(makefile): change gofmt toll to gofumpt

Makefile

@@ -1,6 +1,6 @@
 DIST := dist
 EXECUTABLE := drone-ssh
-GOFMT ?= gofmt "-s"
+GOFMT ?= gofumpt -l -s
 GO ?= go
 
 # for dockerhub
@@ -28,6 +28,9 @@ endif
 all: build
 
 fmt:
+	@hash gofumpt > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
+		$(GO) get -u mvdan.cc/gofumpt; \
+	fi
 	$(GOFMT) -w $(SOURCES)
 
 vet:
@@ -55,6 +58,9 @@ misspell:
 
 .PHONY: fmt-check
 fmt-check:
+	@hash gofumpt > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
+		$(GO) get -u mvdan.cc/gofumpt; \
+	fi
 	@diff=$$($(GOFMT) -d $(SOURCES)); \
 	if [ -n "$$diff" ]; then \
 		echo "Please run 'make fmt' and commit the result:"; \

plugin_test.go

@@ -387,9 +387,7 @@ func TestCommandOutput(t *testing.T) {
 }
 
 func TestWrongFingerprint(t *testing.T) {
-	var (
-		buffer bytes.Buffer
-	)
+	var buffer bytes.Buffer
 
 	plugin := Plugin{
 		Config: Config{