feat: introduce @babel/helper-plugin-utils to ensure babel version

Author: twada

index.js

@@ -10,7 +10,10 @@
  */
 'use strict';
 
-module.exports = function (babel) {
+var declare = require('@babel/helper-plugin-utils').declare;
+
+module.exports = declare(function (api, options, dirname) {
+    api.assertVersion(7);
     return {
         visitor: {
             AssignmentExpression: {
@@ -51,7 +54,7 @@ module.exports = function (babel) {
             }
         }
     };
-};
+});
 
 function replaceAssertIfMatch (node) {
     var target;

package.json

@@ -10,6 +10,7 @@
   "bugs": "https://github.com/power-assert-js/babel-plugin-empower-assert/issues",
   "devDependencies": {
     "@babel/core": "^7.0.0",
+    "@babel/helper-plugin-utils": "^7.0.0",
     "mocha": "^5.0.0",
     "xtend": "^4.0.1"
   },