fix a TextField demo typo

[tangyiyang]

Hi, According to the code: https://github.com/alibaba/LuaViewSDK/blob/58c4a56b24e31643bcec4f569a0aaa8890ca0a9d/IOS/LuaViewSDK/Classes/lvsdk/LVTextField.m#L190

It seems we need to change setText to text if we were going to run the textfield demo on iOS.

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