Removing coveralls integration

This change removes coveralls integration from PyKMIP, specifically
the tox and TravisCI configuration files. codecov will be the
primary coverage tool used going forward.

.travis.yml

@@ -19,9 +19,7 @@ install:
   - pip install tox
   - pip install bandit
   - pip install codecov
-  - pip install coveralls
 script:
   - tox
 after_success:
   - codecov
-  - coveralls

tox.ini

@@ -6,7 +6,6 @@ passenv = TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
 
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-       coveralls
 
 commands =
     coverage run --source=kmip/ --omit=kmip/demos/*,kmip/tests/* -m pytest --strict kmip/tests/unit