add `data` to the argument signature of the key_for_request signature

[fgregg]

For some weird websites, we want to be able to cache post requests. Changing this signature allows us to override key_for_request in our local Scraper class to do so.

[jamesturk]

SGTM, looks like it broke a test, glad to merge once ready

[fgregg]

i think it's httpbin being overloaded. when i run the test suite locally, i'll get some errors in tests that interact with httpbin but i can't reproduce when just running that one test.

[fgregg]

https://pypi.org/project/pytest-httpbin/ looks like it might be a smart idea

[fgregg]

@jamesturk, i made the change to use a local httpbin instance and now all tests are passing.

[jamesturk]

Ah thanks for this, looks great!