fastcache error with test_wester

test_wester fails consistently on 3.4 with 
```bash
PYTHONHASHSEED=1756078925
seed = 45968850
```
(the current failure in master)

Update .travis.yml with `FASTCACHE="false"` when `SPLIT=1/4`

The Python LRU cache does not exhibit this behavior so this is likely a bug in fastcache.  I'll submit another PR once it's fixed.