Singer-tap-appsflyer

* Add organic installations[20](https://github.com/singer-io/tap-appsflyer/pull/20)
* Add Helper Function to remove whitespaces from config and respective unittest[29](https://github.com/singer-io/tap-appsflyer/pull/29)
* Added data restrictions of no more than 90 days from Current date[30](https://github.com/singer-io/tap-appsflyer/pull/30)

* Adds safety try/catch to bookmarking logic for when `attributed_touch_time` does not exist on `installs` stream rows [24](https://github.com/singer-io/tap-appsflyer/pull/24)

* Updates `requests` to version `2.20.0` in response to CVE 2018-18074 [13](https://github.com/singer-io/tap-appsflyer/pull/13)

* Remove `"format": "uri"` from in_app_events schema [12](https://github.com/singer-io/tap-appsflyer/pull/12)

* Fixes infinite loop on `in_app_events` stream [11](https://github.com/singer-io/tap-appsflyer/pull/11)

* Allow booleans to be `None` in traqnsform code [9](https://github.com/singer-io/tap-appsflyer/pull/9)