doc: replace undocumented encoding aliases

Backport-PR-URL: #16421
PR-URL: #16368
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Bryan English <[email protected]>

Author: vsemozhetbyt

doc/api/fs.md

@@ -1284,7 +1284,7 @@ If the file previously was shorter than `len` bytes, it is extended, and the
 extended part is filled with null bytes ('\0'). For example,
 
 ```js
-console.log(fs.readFileSync('temp.txt', 'utf-8'));
+console.log(fs.readFileSync('temp.txt', 'utf8'));
 // Prints: Node.js
 
 // get the file descriptor of the file to be truncated