Makefile: Fix SRC defintion

Current SRC definition only picks up main.go, not all golang source code
of the project. Fix so that 'make fmt" and 'make simplify' can work as
expected.

Makefile

@@ -32,7 +32,7 @@ PKG_GOLANGCI_LINT := github.com/golangci/golangci-lint/cmd/golangci-lint
 export GO111MODULE=on
 
 # go source files, ignore vendor directory
-SRC = $(shell find . -type f -name '*.go' -not -path "./*/*")
+SRC =  *.go cli/*.go
 
 .PHONY: all build build-cross clean fmt simplify check extra-clean install-tools
 
@@ -53,15 +53,12 @@ extra-clean: clean
 	go clean -i $(PKG_GOLANGCI_LINT)
 
 fmt:
-	@gofmt -l -w $(SRC)
-
-simplify:
 	@gofmt -s -l -w $(SRC)
 
 check:
 	@test -z $(shell gofmt -l main.go | tee /dev/stderr) || echo "[WARN] Fix formatting issues with 'make fmt'"
 	@golangci-lint run
-	@go vet ${SRC}
+	@go vet  main.go
 
 # Check for required executables
 HAS_GOX := $(shell command -v gox 2> /dev/null)