`get_matlab()` subsequent calls error

`lru_cache` might not work as expected with `ipykernel`?

```python
# lib.py
def some_function():
  import spm12
  eng = spm12.get_matlab()
  ...
```

```python
# ipython
In[*]: import lib
In[*]: lib.some_function()
In[*]: import spm12
In[*]: spm12.get_matlab()  # error: cannot find matlab session
```


