Do not attempt to deploy library to PyPI on each Travis CI environment

[playpauseandstop]

Build #68 at Travis CI failed cause Travis attempted to deploy (upload) new version of Flask-And-Redis library to PyPI from each Python version, which is wrong.

Need to fix .travis.yml config to allow deploy library only for python 3.7.

[docapotamus]

Hi.

I was just looking for the docs link and saw this. I quickly checked the Travis docs. I think the solution may be:

deploy:
  provider: pypi
  user: playpauseandstop
  password:
    secure: adlnY9sKpfJPdcpnh0SuhQ4iIbZozQ4uNMJ/UgAra4ft4FfiDhYKqqbz58mX0PSKhLcaA0RAeLeesMqqiKrEBRmmQeu7k/pM5kw3Z57B7H/zMIoHDqgbdUMvM3Jf6PZrgx5qat48ECGZHz0ImvQzwfr98i1k+wmJM5on2X6pWgU=
  distributions: sdist bdist_wheel
  on:
    branch: "master"
    python: "3.7"
    tags: true

I thought this may have been hard to test in a PR.