Only run coverage for Python 3.

.travis.yml

@@ -63,8 +63,11 @@ script:
     - "echo 'backend.qt4 : PyQt4' >> $HOME/.matplotlib/matplotlibrc"
 
     # Run all tests
-    - nosetests --exe -v --with-doctest --with-cov --cov skimage --cov-config .coveragerc skimage
-
+    - if [[ $PYVER == '3.x' ]]; then
+    -   nosetests --exe -v --with-doctest --with-cov --cov skimage --cov-config .coveragerc skimage
+    - else
+    -   nosetests --exe -v --with-doctest skimage
+    - fi
     # Run all doc examples
     - export PYTHONPATH=$(pwd):$PYTHONPATH
     - for f in doc/examples/*.py; do $PYTHON "$f"; if [ $? -ne 0 ]; then exit 1; fi done
@@ -74,4 +77,6 @@ script:
     - flake8 --exit-zero --exclude=test_*,six.py skimage doc/examples viewer_examples
 
 after_success:
-    - coveralls
+     - if [[ $PYVER == '3.x' ]]; then
+     -   coveralls
+     - fi