Minor: change a variable name to reduce confusion
Minor: change a variable name to reduce confusion

I found the name of this variable confusing (`this.views` is elsewhere
in this function) so I renamed it.

`npm test` passes after this minor change.

braintree/braintree-web-drop-in,braintree/braintree-web-drop-in,braintree/braintree-web-drop-in