Update Performance.md

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Closes https://github.com/facebook/react-native/pull/10484

Differential Revision: D4057708

Pulled By: javache

fbshipit-source-id: e38216092195e5a38bd3afb43c4521cc4edb66ba

docs/Performance.md

@@ -37,7 +37,7 @@ generate that frame within the allotted 16.67ms, then you will "drop a
 frame" and the UI will appear unresponsive.
 
 Now to confuse the matter a little bit, open up the developer menu in
-your app and toggle `Show FPS Monitor`. You will notice that there are
+your app and toggle `Show Perf Monitor`. You will notice that there are
 two different frame rates.
 
 #### JavaScript frame rate