test: import plugin instead of specifc rule

This enhances the test to catch any issue that would break `index.js`
from being able to correctly import the default export of
`rules/no-use-extend-native.js`.

test/test.js

@@ -1,10 +1,12 @@
 'use strict'
 import AvaRuleTester from 'eslint-ava-rule-tester'
-import noUseExtendNativeRule from '../rules/no-use-extend-native'
+import noUseExtendNative from '..'
 import test from 'ava'
 
 const ruleTester = new AvaRuleTester(test)
 
+const noUseExtendNativeRule = noUseExtendNative.rules['no-use-extend-native']
+
 ruleTester.run('no-use-extend-native/no-use-extend-native', noUseExtendNativeRule, {
   valid: [
     'error.plugin',