doc: small grammar correction

This commit improves the grammar of one sentence in the ESM
documentation.

PR-URL: #28669
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Jiawen Geng <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: cjihrig

doc/api/esm.md

@@ -278,8 +278,8 @@ These CommonJS variables are not available in ES modules.
 
 `require` can be imported into an ES module using [`module.createRequire()`][].
 
-An equivalent for variable `__filename` and `__dirname` can be created inside
-each file with [`import.meta.url`][].
+Equivalents of `__filename` and `__dirname` can be created inside of each file
+via [`import.meta.url`][].
 
 ```js
 import { fileURLToPath } from 'url';