Update Performance.md

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[1]: https://medium.com/martinkonicek/what-is-a-test-plan-8bfc840ec171#.y9lcuqqi9
[2]: https://code.facebook.com/cla
[3]: https://travis-ci.org/facebook/react-native
[4]: http://circleci.com/gh/facebook/react-native
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Closes https://github.com/facebook/react-native/pull/14204

Differential Revision: D5137182

Pulled By: javache

fbshipit-source-id: a9de972432618b8a3e5fece3e7dc4d94bad2c6cc

docs/Performance.md

@@ -107,7 +107,7 @@ One case where I have used this is for animating in a modal (sliding down from t
 
 Caveats:
 
-- LayoutAnimation only works for fire-and-forget animations ("static" animations) -- if it must be be interruptible, you will need to use `Animated`.
+- LayoutAnimation only works for fire-and-forget animations ("static" animations) -- if it must be interruptible, you will need to use `Animated`.
 
 ### Moving a view on the screen (scrolling, translating, rotating) drops UI thread FPS
 
@@ -185,7 +185,7 @@ The first step for debugging this jank is to answer the fundamental question of
 For that, we'll be using a standard Android profiling tool called `systrace`.
 
 `systrace` is a standard Android marker-based profiling tool (and is installed when you install the Android platform-tools package).
-Profiled code blocks are surrounded by markers start/end markers which are then visualized in a colorful chart format.
+Profiled code blocks are surrounded by start/end markers which are then visualized in a colorful chart format.
 Both the Android SDK and React Native framework provide standard markers that you can visualize.
 
 #### 1. Collecting a trace
@@ -321,7 +321,7 @@ And many times, you'll want to look into [shouldComponentUpdate](https://faceboo
 
 If you identified a native UI problem, there are usually two scenarios:
 
-1. the UI you're trying to draw each frame involves to much work on the GPU, or
+1. the UI you're trying to draw each frame involves too much work on the GPU, or
 2. You're constructing new UI during the animation/interaction (e.g. loading in new content during a scroll).
 
 ##### Too much GPU work