Exit with 2 if misspelling found

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

Makefile

@@ -94,12 +94,7 @@ misspell-check:
 	@hash misspell > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
 		go get -u github.com/client9/misspell/cmd/misspell; \
 	fi
-	@diff=$$(misspell $(GOFILES)); \
-	if [ -n "$$diff" ]; then \
-		echo "Please fix the misspelling:"; \
-		echo "$${diff}"; \
-		exit 1; \
-	fi;
+	misspell -error $(GOFILES)
 
 test: fmt-check
 	for PKG in $(PACKAGES); do go test -v -cover -coverprofile $$GOPATH/src/$$PKG/coverage.txt $$PKG || exit 1; done;