Fix Mentor Request table tests

[leenyburger]

Description of changes

• Removed Airtable cassettes from old implementation
• Recorded new VCR cassettes for the following files:

1. test/cassettes/airtable/client/get_records_successful.yml
2. test/cassettes/airtable/client/post_record_successful.yml
3. test/cassettes/airtable/mentorship/post_multiple_successful.yml
4. test/cassettes/airtable/mentorship/post_successful.yml

• Updated Apiary to include new email field
• Updated Skillset options in test to account for new multiple choice options on Skillsets in Airtable

[leenyburger]

@hpjaj Updated. That was my personal API key and I deleted it from Airtable.

[jjhampton]

Going to merge this, TravisCI build has passed but isn't updating on GitHub: https://travis-ci.org/OperationCode/operationcode_backend/builds/415961638