[LinearTransformationScene] the unit vector j doesn't move with the same acceleration as the y-axis

Nobody has claimed this yet.

## Description of bug / unexpected behavior

The unit vector j and the y-axis have different speeds. See video below.

## Expected behavior

They are always in the same line during transformation.

## How to reproduce the issue

Code for reproducing the problem

```py
class Test1(LinearTransformationScene):
def __init__(self):
LinearTransformationScene.__init__(self, include_background_plane=False)

def construct(self):
matrix = [[1, 3], [-2, 0]]
self.apply_matrix(matrix)
self.wait()
```

## Additional media files

Images/GIFs

https://user-images.githubusercontent.com/7588612/124348525-fdc9fc00-dc1c-11eb-873e-055a2a2ccdb2.mp4

## Logs
Terminal output

```
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## System specifications

Doesn't seem to be relevant.

System Details

- OS (with version, e.g Windows 10 v2004 or macOS 10.15 (Catalina)):
- RAM:
- Python version (`python/py/python3 --version`):
- Installed modules (provide output from `pip list`):
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LaTeX details

+ LaTeX distribution (e.g. TeX Live 2020):
+ Installed LaTeX packages:

FFMPEG

Output of `ffmpeg -version`:

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```

## Additional comments

Start with the LinearTransformationScene and its apply_matrix entry point, using the reproducer in the issue to observe the unit vector j and y-axis during the transformation. Trace how both objects are animated and verify the result with the provided matrix: they should remain on the same line throughout the transformation.

Written by the indexing model from the issue text.