Merge pull request sendgrid#113 from sendgrid/travis_ci_prism_fix

Fix Travis CI Prism functionality, update deprecated File.exists

Version Bump v4.0.5: Pull sendgrid#110, fixed Issue sendgrid#109 Auto…

…mates StopLight.io Prism mock server locally & on Travis CI

Version Bump v4.0.4: Pull sendgrid#72: remove ruby 2.2 requirement

Merge branch 'master' of https://github.com/sendgrid/sendgrid-ruby

Version Bump v4.0.2: Example and USAGE DELETE calls were missing exam…

…ple payloads

Version Bump v4.01: Added Troubleshooting section

CHANGELOG formatting

Version Bump v3.0.7: README documentation updates

Version Bump v3.0.6: Update docs, unit tests and examples to include …

…Sender ID

Version Bump v3.0.5: swagger/oai updates + accept header fix