Update release command

Makefile

@@ -1,4 +1,4 @@
-VERSION_REGEX  := 's/(v[0-9\.]+)/$(version)'
+VERSION_REGEX  := 's/(v[0-9\.]+)/$(version)/g'
 
 build:
 	go build -o smug *.go
@@ -14,7 +14,7 @@ release:
 ifndef GITHUB_TOKEN
 	$(error GITHUB_TOKEN is not defined)
 endif
-	sed -i '$(VERSION_REGEX)' main.go > main.go
+	sed -E -i.bak $(VERSION_REGEX) 'main.go'
 	git commit -am '$(version)'
 	git tag -a $(version) -m '$(version)'
 	git push origin $(version)