fix bug in unittest script

It appears that some versions of numpy do not like the dtype string `'b1'` which causes the unittests to fail incorrectly. (Note that `'b'` in numpy is defined to be 1 byte long, so `'b1'` is redundant in some sense, not that this matters.) When I declare an array with type `'b1'` with my numpy 1.9.0 I get back
```python
In [5]: d = np.zeros(1,dtype=[('logical','b1')])
In [6]: d.dtype
Out[6]: dtype([('logical', '?')])
````
The `'?'` indicates a problem. 

When setting `'b1'` to `'b'`, I get
```python
In [7]: d = np.zeros(1,dtype=[('logical','b')])
In [8]: d.dtype
Out[8]: dtype([('logical', 'i1')])
```
which defaults to the correct type. 

With this change, all of the unittests pass.