Move codecov invocation from Tox to Travis

This avoids errors when running Tox locally.
Also display line numbers missing test coverage.

.travis.yml

@@ -14,6 +14,9 @@ python:
 install:
   - pip install -U pip setuptools
   - pip install tox-travis pre-commit
+  - pip install codecov
 script:
   - tox
   - if [[ $TRAVIS_PYTHON_VERSION != 2.6 ]]; then pre-commit run --all-files; fi
+after_success:
+  - codecov

setup.py

@@ -5,6 +5,7 @@ install_requires = [
     'pytz',
     'six',
     'python-dateutil',
+    'requests',
 ]
 
 setup(

tox.ini

@@ -8,10 +8,8 @@ deps =
     pytest
     pytest-cov
     coverage
-    codecov
 commands =
-    py.test --cov=stix2 stix2/test/
+    py.test --cov=stix2 stix2/test/ --cov-report term-missing
-    codecov
 
 passenv = CI TRAVIS TRAVIS_*