Update .travis.yml

Totally neutering Travis because nosetests keeps dying on their system.

```
nosetests test

test test_builtin failed -- Traceback (most recent call last):
File "/opt/python/2.7.6/lib/python2.7/test/test_builtin.py", line 471, in test_execfile
execfile(TESTFN, globals)
IOError: [Errno 2] No such file or directory: '@test_1496_tmp'
Skipping test_concat because of memory constraint
Skipping test_optimized_concat because of memory constraint
test test_cpickle failed -- multiple errors occurred
```