fix: Failed to replaces hash when loader is a actual file name.

For example:
```html
<link rel="manifest" href="/manifest.json">
```
```
{
    test: /manifest.json$/,
    loader: 'file-loader',
    options: {
      name: `[name]-[hash:${fileHashLength}].[ext]`
    }
  }

new ReplaceHashWebpackPlugin({
    src: `**/*.html`,
    exts: ['js', 'css', 'png', 'json']
  })
```

index.js

@@ -66,7 +66,7 @@ ReplaceHashPlugin.prototype.apply = function (compiler) {
             break;
           default:
             compiler.options.module.rules.forEach(function(rule) {
-              if (rule.test.test(ext)) {
+              if (rule.test.toString().indexOf(ext) > -1) {
                 var query = rule.query || rule.options;
                 if (rule.use) {
                   rule.use.forEach(function(use) {