drop coveralls installation from travis ci

.travis.yml

 install:
   - cd tracim && python setup.py develop; cd -
   - pip install -r install/requirements.txt; echo
-  - pip install coveralls
 
 before_script:
   - cp ${TRAVIS_BUILD_DIR}/tracim/development.ini.base ${TRAVIS_BUILD_DIR}/tracim/development.ini
 
 # command to run tests
 script: "cd ${TRAVIS_BUILD_DIR}/tracim && nosetests -c ${TRAVIS_BUILD_DIR}/tracim/test.ini -v --with-coverage --cover-package=tracim --cover-erase"
-
-after_success:
-- coveralls