修改UItextField输入框placeholder的字体默认颜色和大小，采用KVC方式设置

修改UItextField输入框placeholder的字体默认颜色和大小，采用KVC方式设置

[_textField setValue:[UIColor getCommonColorWithColorType:ColorWhiteType] forKeyPath:@"_placeholderLabel.textColor"];

    [_textField setValue:[UIFont getCommonFontWithFontType:SmallFontType] forKeyPath:@"_placeholderLabel.font"];