Bump to Go v. 1.14 as requirement

Makefile

@@ -6,7 +6,7 @@ all: build
 unexport GOFLAGS
 
 GOVERSION:=$(shell go version | cut -d' ' -f 3 | cut -d. -f 2)
-ifeq ($(shell expr $(GOVERSION) \< 13), 1)
+ifeq ($(shell expr $(GOVERSION) \< 14), 1)
 $(warning Your Golang version is go 1.$(GOVERSION))
 $(error Update Golang to version $(shell grep '^go' go.mod))
 endif