Move vcr cassettes to default location

fixture/vcr_cassettes/animation_flip_coin_getters.json

fixture/vcr_cassettes/animation_flip_coin_graphics.json

fixture/vcr_cassettes/bad_request.json

fixture/vcr_cassettes/description.json

fixture/vcr_cassettes/digest_hmac.json

fixture/vcr_cassettes/flip_coin.json

fixture/vcr_cassettes/github_package_not_found.json

fixture/vcr_cassettes/no_endpoint_configured.json

fixture/vcr_cassettes/prepare.json

fixture/vcr_cassettes/response_with_na_values.json

mix.exs

...ttp_potion_vcr_cassettes/animation_flip_coin_getters.json

...tp_potion_vcr_cassettes/animation_flip_coin_graphics.json

test/fixtures/http_potion_vcr_cassettes/bad_request.json

test/fixtures/http_potion_vcr_cassettes/description.json

test/fixtures/http_potion_vcr_cassettes/digest_hmac.json

test/fixtures/http_potion_vcr_cassettes/flip_coin.json

...s/http_potion_vcr_cassettes/github_package_not_found.json

test/fixtures/http_potion_vcr_cassettes/prepare.json

...es/http_potion_vcr_cassettes/response_with_na_values.json