Fix "similar-code" issue in smtpapi/__init__.py

[thinkingserious]

Similar blocks of code found in 4 locations. Consider refactoring.

Check the issues mentioned here:
https://codeclimate.com/github/sendgrid/smtpapi-python/smtpapi/__init__.py

[Bezzy1999]

Hi I'd like to work on this, should I just create a pr? Thanks.

[thinkingserious]

Hi @Bezzy1999,

Sorry for the super delayed response :(

It looks like @Tranquilled has already submitted a PR for this.

[childish-sambino]

Fixed by #53