build: use npx in Makefile itself

Author: zkat

Makefile

@@ -12,8 +12,8 @@ libnpx.1: README.md
 	npm run docs
 
 bin/package.json: package.json bin/package.template.json
-	cat bin/package.template.json | json -e "this.version = '$$(cat package.json | json version)'" > $@
-	json -I -f $@ -e "this.dependencies.libnpx = '$$(cat $@ | json version)'"
+	cat bin/package.template.json | npx json -e "this.version = '$$(cat package.json | npx json version)'" > $@
+	npx json -I -f $@ -e "this.dependencies.libnpx = '$$(cat $@ | npx json version)'"
 
 bin/node_modules: bin/package.json
 	cd bin && npm i