Update excel.py to output OrderedDict instead of dict
It should fix https://github.com/pydata/pandas/issues/9930

This does seem like a good idea. Can you write a test to verify that it works?
 Sorry but I don't understand why CI raises this error for Python 2.x

```
Error: HTTPError: 403 Client Error: Forbidden: http://conda.binstar.org/pandas/linux-64/bigquery-2.0.17-py27_0.tar.bz2
```

I also don't understand why "OrderedDict should be imported from `pandas.compat` instead to ensure backwards" because according https://docs.python.org/2/library/collections.html collections exists since Python 2.4 "New in version 2.4." but maybe collections is existing since 2.4 but not OrderedDict.

I noticed that a pip package exists https://pypi.python.org/pypi/ordereddict but I don't know how to automatically install it only for Python < 2.7 (so 2.6 in our case)
 I think that CI failure is something spurious related to binstar. I just retriggered the Travis tests for this PR -- hopefully we won't see that error message again.

As for OrderedDict, indeed it first appeared in Python 2.7. We already have a copy of OrderedDict bundled with pandas for exactly this reason. To use it, just use `from pandas.compat import OrderedDict`.
 Follow-up: #9944
