doc: fix a function name in repl.md

`eval` => `myEval` to not shadow the global `eval`

PR-URL: https://github.com/nodejs/node/pull/10244
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/repl.md

@@ -186,7 +186,7 @@ multi-line input, the eval function can return an instance of `repl.Recoverable`
 to the provided callback function:
 
 ```js
-function eval(cmd, context, filename, callback) {
+function myEval(cmd, context, filename, callback) {
   let result;
   try {
     result = vm.runInThisContext(cmd);