# ValueError: Unknown projection '3d'

I'm using **matplotlib** and want to plot 3D points, but I get an error like this

```
ValueError Traceback (most recent call last)
<ipython-input-8-13a022ef9a21> in <module>()
1 fig = plt.figure()
----> 2 ax = fig.add_subplot(111, projection='3d')
~/.local/lib/python3.5/site-packages/matplotlib/figure.py in add_subplot(self, *args, **kwargs)
1347 else:
1348 projection_class, kwargs, key = process_projection_requirements(
-> 1349 self, *args, **kwargs)
1350
1351 # try to find the axes with this key in the stack
~/.local/lib/python3.5/site-packages/matplotlib/projections/__init__.py in process_projection_requirements(figure, polar, projection, *args, **kwargs)
79
80 if isinstance(projection, str) or projection is None:
---> 81 projection_class = get_projection_class(projection)
82 elif hasattr(projection, '_as_mpl_axes'):
83 projection_class, extra_kwargs = projection._as_mpl_axes()
~/.local/lib/python3.5/site-packages/matplotlib/projections/__init__.py in get_projection_class(projection)
58 return projection_registry.get_projection_class(projection)
59 except KeyError:
---> 60 raise ValueError("Unknown projection %r" % projection)
61
62
ValueError: Unknown projection '3d'
```

What's wrong with this?