Change doc link to point to AnimatedValueXY

Summary:
Currently goes to the same page

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Online doc was not helpful because the link kept going to the wrong page. Someone told me to make a pull request

Documentation change
Go to original link https://facebook.github.io/react-native/docs/animated.html#animatedvaluexy
See that it does not have any info on valuexy

Go to https://facebook.github.io/react-native/releases/next/docs/animatedvaluexy.html
See that the page loads and has information about valuexy

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[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
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 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
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Closes https://github.com/facebook/react-native/pull/16999

Differential Revision: D6467512

Pulled By: shergin

fbshipit-source-id: 69887e34446c3ea57ad831ed870be4e1a8a7a514

Libraries/Animated/src/AnimatedImplementation.js

@@ -523,7 +523,7 @@ module.exports = {
   /**
    * 2D value class for driving 2D animations, such as pan gestures.
    *
-   * See http://facebook.github.io/react-native/docs/animated.html#valuexy
+   * See https://facebook.github.io/react-native/releases/next/docs/animatedvaluexy.html
    */
   ValueXY: AnimatedValueXY,
   /**