Fix typo in comments for LoopController (#1489)

Summary: Pull Request resolved: https://github.com/facebook/folly/pull/1489

Differential Revision: D25156288

Pulled By: yfeldblum

fbshipit-source-id: 01c9e6898158e9651367144c22f215ef75ff7ae3

folly/fibers/LoopController.h

@@ -41,7 +41,7 @@ class LoopController {
 
   /**
    * Called by FiberManager to schedule the loop function run
-   * at some point in the futufre.
+   * at some point in the future.
    */
   virtual void schedule() = 0;