doc: fix link on timers.md

PR-URL: https://github.com/nodejs/node/pull/8488
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/timers.md

@@ -22,7 +22,7 @@ This object is created internally and is returned from [`setTimeout()`][] and
 [`setInterval()`][]. It can be passed to [`clearTimeout`][] or
 [`clearInterval()`][] (respectively) in order to cancel the scheduled actions.
 
-By default, when a timer is scheduled using either [`setTimeout`] or
+By default, when a timer is scheduled using either [`setTimeout()`][] or
 [`setInterval()`][], the Node.js event loop will continue running as long as the
 timer is active. Each of the `Timeout` objects returned by these functions
 export both `timeout.ref()` and `timeout.unref()` functions that can be used to