`GPUArray.minimum` fails for `bool` arguments

Here's an MWE

```python
>>> import numpy as np
>>> import pycuda.autoinit
>>> import pycuda.gpuarray as gpuarray
>>> a = np.array(True)
>>> b = np.array(False)
>>> a_gpu = gpuarray.to_gpu(a)
>>> b_gpu = gpuarray.to_gpu(b)
>>> result_np = np.minimum(a, b)
>>> print(result_np)
>>> gpuarray.minimum(a_gpu, b_gpu)
```