Fixed: self.placeholder does not update it's position when set textView's textContainerInset

[meigesir]

the default vlue of textContainerInset is (8, 0, 8, 0) For example:

    UIEdgeInsets edgeInsets = _textView.internalTextView.textContainerInset;
    edgeInsets.left = 8;
    edgeInsets.right = 8;
    _textView.internalTextView.textContainerInset = edgeInsets;