System information

• Cantera version: 2.5.0a4
• OS: Ubuntu Xenial with default packages
• Python/MATLAB version: 3.5.2

Expected behavior

scons test works out of the box, after successful scons build

Actual behavior

Test fails

Traceback (most recent call last):
  File "/src/test/python/runCythonTests.py", line 35, in <module>
    from cantera.test.utilities import unittest
  File "/src/build/python/cantera/test/__init__.py", line 13, in <module>
    from .test_convert import *
  File "/src/build/python/cantera/test/test_convert.py", line 8, in <module>
    from cantera import ck2cti, ck2yaml, cti2yaml, ctml2yaml
  File "/src/build/python/cantera/ck2yaml.py", line 100, in <module>
    yaml.RoundTripRepresenter.add_representer(float, represent_float)
AttributeError: module 'ruamel.yaml' has no attribute 'RoundTripRepresenter'

To Reproduce

Steps to reproduce the behavior:

1. Install Xenial (ubuntu 16.04 - same as current Travis) and update apt-get update
2. Install default ruamel-yaml via apt-get install python3-ruamel.yaml (which has version '0.10.23')
3. See above failure

Additional context

The alternate pip3 install ruamel-yaml works (version '0.16.10') ...

To resolve, a minimum version for ruamel.yaml appears to be necessary.