Travis errors on Python3.6 PYTHON_PLUS=True

[jGaboardi]

Since 12/5 the Python 3.6 PYTHON_PLUS=True build on Travis has been failing with the following error message:

The job exceeded the maximum log length, and has been terminated.

Although it seems that no defaults had been changed between this build and the previous build, the Travis documentation recommends changing the maximum log length.

It is unclear at this point if this is a Travis issue that will clear up on its own or something that we have more control over.

[jGaboardi]

related to pysal/spaghetti#249?

[jGaboardi]

addressed in #140