Add a check in the makefile to ensure a minimum version of go is installed (#383)

Makefile

@@ -1,8 +1,16 @@
+GOMINVERSION = 1.16
 NEBULA_CMD_PATH = "./cmd/nebula"
 BUILD_NUMBER ?= dev+$(shell date -u '+%Y%m%d%H%M%S')
 GO111MODULE = on
 export GO111MODULE
 
+# Ensure the version of go we are using is at least what is defined in GOMINVERSION at the top of this file
+GOVERSION := $(shell go version | awk '{print substr($$3, 3)}')
+GOISMIN := $(shell expr "$(GOVERSION)" ">=" "$(GOMINVERSION)")
+ifneq "$(GOISMIN)" "1"
+$(error "go version $(GOVERSION) is not supported, upgrade to $(GOMINVERSION) or above")
+endif
+
 LDFLAGS = -X main.Build=$(BUILD_NUMBER)
 
 ALL_LINUX = linux-amd64 \
@@ -24,6 +32,8 @@ ALL = $(ALL_LINUX) \
 	freebsd-amd64 \
 	windows-amd64
 
+
+
 all: $(ALL:%=build/%/nebula) $(ALL:%=build/%/nebula-cert)
 
 release: $(ALL:%=build/nebula-%.tar.gz)

go.mod

@@ -1,6 +1,6 @@
 module github.com/slackhq/nebula
 
-go 1.12
+go 1.16
 
 require (
 	github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239