[#177] Makefile: build with neo-go from go.mod

Currently compiler version and test/interop version are decoupled.
It would be nice to use the compiler from go.mod by default
as this is the version our contracts are tested on.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

Makefile

@@ -1,12 +1,13 @@
 #!/usr/bin/make -f
 
 SHELL=bash
-NEOGO?=neo-go
+GOBIN ?= $(shell go env GOPATH)/bin
+NEOGO ?= $(GOBIN)/cli
 VERSION?=$(shell git describe --tags)
 
-.PHONY: all build clean test
+.PHONY: all build clean test neo-go
 .PHONY: alphabet mainnet morph nns sidechain
-build: all
+build: neo-go all
 all: sidechain mainnet
 sidechain: alphabet morph nns
 
@@ -34,6 +35,10 @@ morph: $(foreach sc,$(morph_sc),$(sc)/$(sc)_contract.nef)
 mainnet: $(foreach sc,$(mainnet_sc),$(sc)/$(sc)_contract.nef)
 nns: $(foreach sc,$(nns_sc),$(sc)/$(sc)_contract.nef)
 
+neo-go:
+	@go list -f '{{.Path}}/...@{{.Version}}' -m github.com/nspcc-dev/neo-go \
+		| xargs go install -v
+
 test:
 	@go test ./tests/...