Fix typo in ScrollView childLayoutProps error message

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Closes https://github.com/facebook/react-native/pull/6454

Differential Revision: D3049074

Pulled By: sahrens

fb-gh-sync-id: 61d085bb5c7bedf80204cdfb94e5c23542e15333
shipit-source-id: 61d085bb5c7bedf80204cdfb94e5c23542e15333

Libraries/Components/ScrollView/ScrollView.js

@@ -431,7 +431,7 @@ var ScrollView = React.createClass({
       invariant(
         childLayoutProps.length === 0,
         'ScrollView child layout (' + JSON.stringify(childLayoutProps) +
-          ') must by applied through the contentContainerStyle prop.'
+          ') must be applied through the contentContainerStyle prop.'
       );
     }