Merge branch 'master' into bugfix_and_refactoring

.travis.yml

@@ -13,7 +13,7 @@ install:
   - "sudo apt-get install -y mongodb-org" 
   - "sudo service mongod start"
   - "python setup.py -q install"
-  - "pip install pytest-pep8 pytest-cov codecov"
+  - "pip install --upgrade pytest pytest-pep8 pytest-cov codecov"
 # command to run tests
 script: "pytest --cov-config .coveragerc --cov=./"
 after_success: