qt.qpa.plugin problem

Hello i tried to make instalation inside virtualenv with python 3.6.7, Here the steps i made:

`pip install mayavi` - success
`pip install PyQt5` - success
`pip install pysurfer` - success
`jupyter nbextension install --py mayavi --user`
`jupyter nbextension install --py mayavi --user`

Then in Ipython is try next:

```
In [2]: %gui qt

In [3]: import numpy as np

In [4]: from mayavi import mlab
```

And the error is:

```
qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb.

Aborted (core dumped)
```

How to resolve it?