doc: var -> const / let in the console.md

PR-URL: https://github.com/nodejs/node/pull/10451
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/console.md

@@ -88,7 +88,7 @@ const errorOutput = fs.createWriteStream('./stderr.log');
 // custom simple logger
 const logger = new Console(output, errorOutput);
 // use it like console
-var count = 5;
+const count = 5;
 logger.log('count: %d', count);
 // in stdout.log: count 5
 ```
@@ -217,7 +217,7 @@ values similar to printf(3) (the arguments are all passed to
 [`util.format()`][]).
 
 ```js
-var count = 5;
+const count = 5;
 console.log('count: %d', count);
 // Prints: count: 5, to stdout
 console.log('count:', count);
@@ -248,7 +248,7 @@ prints the result to `stdout`:
 
 ```js
 console.time('100-elements');
-for (var i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
   ;
 }
 console.timeEnd('100-elements');