Get version from version.py instead of version.txt

[lipis]

When deploying to App Engine using the zipped libraries, reading the txt file is not possible and I'm getting the following error:

cannot import name __version__ (/base/data/home/apps/e~dionysus-app/20190525t145530.418433277209349498/control/error.py:25)
Traceback (most recent call last):
  File "lib.zip/flask/app.py", line 1832, in full_dispatch_request
    rv = self.dispatch_request()
  File "lib.zip/flask/app.py", line 1818, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/base/data/home/apps/e~dionysus-app/20190525t145530.418433277209349498/auth/auth.py", line 261, in decorated_function
    return f(*args, **kwargs)
  File "/base/data/home/apps/e~dionysus-app/20190525t145530.418433277209349498/control/places/supply.py", line 288, in place_supply_order_email
    response = task.place_supply_order(place_db, supply_db, vendor_db)
  File "/base/data/home/apps/e~dionysus-app/20190525t145530.418433277209349498/task.py", line 267, in place_supply_order
    return send_sendgrid_email(subject, body, to, place_db.name)
  File "/base/data/home/apps/e~dionysus-app/20190525t145530.418433277209349498/task.py", line 43, in send_sendgrid_email
    sendgrid_client = sendgrid.SendGridAPIClient(config.CONFIG_DB.sendgrid_api_key)
  File "lib.zip/sendgrid/sendgrid.py", line 58, in __init__
    from . import __version__
ImportError: cannot import name __version__

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them
• I updated my branch with the master branch
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

I reverted the reading of the version how it was before the version 6, and it works as expected.

Check the PR without the whitespaces: https://github.com/sendgrid/sendgrid-python/pull/807/files?w=1

[codecov]

Codecov Report

Merging #807 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #807      +/-   ##
==========================================
+ Coverage      80%   80.02%   +0.01%     
==========================================
  Files          69       70       +1     
  Lines        2016     2018       +2     
  Branches      338      339       +1     
==========================================
+ Hits         1613     1615       +2     
  Misses        204      204              
  Partials      199      199

Impacted Files	Coverage Δ
sendgrid/version.py	100% <100%> (ø)

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[thinkingserious]

Hello @lipis,

Thanks again for the PR!

We want to show our appreciation by sending you some swag. Could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX

[lipis]

Thank you for accepting that! By any chance we can have a new release soon?

[thinkingserious]

Hello @lipis,

I can't make any promises on a release date, but we are generally moving towards a more predictable cadence.

Thanks again for your support!

With Best Regards,

Elmer