EasyPost no method api_key

[embold-tyler]

After updating the gem, a new error prevents the site from starting if the initializer has EasyPost.api_key = and returns undefined method 'api_key=' for EasyPost:Module (NoMethodError)

EasyPost changed the way the client object is instantiated, so it no longer takes a global api_key but instead accepts the api_key when creating a new Client object per instructions here: https://github.com/EasyPost/easypost-ruby/blob/86b2575006f6fd3703b370cc00d72c3bb5b9d724/UPGRADE_GUIDE.md?plain=1#L28