Use pylint 1.1.0 on Travis CI

This should minimise differences between `make check` on developer's
machines and Travis CI. 1.1.0 is the same version as in Ubuntu 14.04.

Pylint 1.x knows about namedtuple members[1] so we no longer have to
ignore E1101 errors regarding stbt.Position, stbt._Rect, stbt._Size,
and stbt.Region.

[1] http://www.logilab.org/revision/148201