Fix callback function type warnings in timers.js
Fix callback function type warnings in timers.js

Closure compiler produced the following warnings:

timers.js:26: WARNING - Bad type annotation. missing opening (
 * @param {function} callback
                   ^

timers.js:39: WARNING - Bad type annotation. missing opening (
 * @param {function} callback
                   ^

Fix by adding argument types to the callback functions.

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

dcodeIO/node.js-closure-compiler-externs,keunwoo/node.js-closure-compiler-externs