Class name "m180824_090744_create_notification_table" is not in StudlyCaps format
Classes in PHP are usually named in CamelCase.
In camelCase names are written without any punctuation, the start of each new word
being marked by a capital letter. The whole name starts with a capital letter as well.
Thus the name database provider becomes DatabaseProvider.
You can fix this by adding a namespace to your class:
When choosing a vendor namespace, try to pick something that is not too generic to avoid conflicts with other libraries.