doc: fix closing parenthesis

PR-URL: nodejs#41190
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Derek Lewis <DerekNonGeneric@inf.is>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>

doc/api/fs.md

@@ -91,7 +91,7 @@ unlink('/tmp/hello', (err) => {
 
 The callback-based versions of the `fs` module APIs are preferable over
 the use of the promise APIs when maximal performance (both in terms of
-execution time and memory allocation are required).
+execution time and memory allocation) is required.
 
 ## Synchronous example