Fixed "constants" typo

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[DOCS][MINOR][JSTimers.js] Fixed "constants" typo
Closes https://github.com/facebook/react-native/pull/16559

Differential Revision: D6184938

Pulled By: shergin

fbshipit-source-id: d16822d3885c6439239102df2790f5dbf5271a19

Libraries/Core/Timers/JSTimers.js

@@ -44,7 +44,7 @@ export type JSTimerType =
   | 'setImmediate'
   | 'requestIdleCallback';
 
-// These timing contants should be kept in sync with the ones in native ios and
+// These timing constants should be kept in sync with the ones in native ios and
 // android `RCTTiming` module.
 const FRAME_DURATION = 1000 / 60;
 const IDLE_CALLBACK_FRAME_DEADLINE = 1;