Fix "similar-code" issue in sendgrid/helpers/mail/mail.py

[thinkingserious]

Similar blocks of code found in 6 locations. Consider refactoring.

https://codeclimate.com/github/sendgrid/sendgrid-python/sendgrid/helpers/mail/mail.py#issue_59f639d0343eae000100008c

[lifez]

@thinkingserious Does this issue need to be done?

[thinkingserious]

Hi @lifez,

Sorry, I should have closed this. I will be incorporating this change in the next version of this SDK.

Thanks for checking!

With Best Regards,

Elmer