This covers cases where we call 'cancel' the very first time,
even if no Toast had ever been displayed beforehand.

* Update fluttertoast.podspec

add s.dependency 'Toast'

* Delete UIView+Toast.h

* Delete UIView+Toast.m

* Fix UIView+Toast.o duplicate symbols

Co-authored-by: yongshuai.kang <yongshuai.kang@zhaopin.com.cn>

* Added new option for ToastGravity called SNACKBAR which renders toast message much like a SnackBar widget does

* minor fix

Co-authored-by: 郭智强 <cook.guo@ximalaya.com>

1.Fixed opening the photo gallery, pick a photo or press cancel, then go back to the app, the toast message can no longer be displayed. (#209)

2.Fixed if the keyboard disappear, the toast disappear at once, because the window where the keyboard is is gone.

Co-authored-by: 冯勇海 <2206728426@qq.com>