Skip ci with pyqt4v2 because of unknown error
```
_______________ ERROR collecting tests/labelme_tests/test_app.py _______________
tests/labelme_tests/test_app.py:5: in <module>
import labelme.app
/usr/share/miniconda/envs/test/lib/python2.7/site-packages/labelme/__init__.py:6: in <module>
from qtpy import QT_VERSION
/usr/share/miniconda/envs/test/lib/python2.7/site-packages/qtpy/__init__.py:237: in <module>
from . import QtDataVisualization as QtDatavisualization
/usr/share/miniconda/envs/test/lib/python2.7/site-packages/qtpy/QtDataVisualization.py:22: in <module>
raise PythonQtError('No Qt bindings could be found')
E PythonQtError: No Qt bindings could be found
```
Kentaro Wada