doc: fix a typo in __dirname section

PR-URL: https://github.com/nodejs/node/pull/6473
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Robert Lindstaedt <robert.lindstaedt@gmail.com>

doc/api/globals.md

@@ -38,7 +38,7 @@ For instance, given two modules: `a` and `b`, where `b` is a dependency of
 
 References to `__dirname` within `b.js` will return
 `/Users/mjr/app/node_modules/b` while references to `__dirname` within `a.js`
-will return `/Users/mj/app`.
+will return `/Users/mjr/app`.
 
 ## \_\_filename