More descriptive TypeError from #dot

The `#dot` method gives the following error if you don't supply it the correct type:
```
/ruby-2.3.3/gems/nmatrix-lapacke-0.2.4/lib/nmatrix/lapack_ext_common.rb:66:in `dot': expected NMatrix on left-hand side of operation (TypeError)
```

A good error message should tell us the wrong type that is being passed too for easier debugging.