[ReactNative] Unbreak flow errors

Libraries/Components/TextInput/TextInput.js

@@ -407,7 +407,7 @@ var TextInput = React.createClass({
     }
   },
 
-  getChildContext: function() {
+  getChildContext: function(): Object {
     return {isInAParentText: true};
   },
 

Libraries/Text/Text.js

@@ -179,7 +179,7 @@ var Text = React.createClass({
     return PRESS_RECT_OFFSET;
   },
 
-  getChildContext: function() {
+  getChildContext: function(): Object {
     return {isInAParentText: true};
   },