Pandas deprecation warning when writing ply file

**Describe the bug**
When I try to write a ply file, I get a deprecation warning on pandas 2.1.0 (python 3.10).

**To Reproduce**
Steps to reproduce the behavior:
1. Just read and write a file:
```python

from pyntcloud import PyntCloud
my_point_cloud = PyntCloud.from_file("c:/temp/test_in.ply")
my_point_cloud.to_file("c:/temp/test.ply")
```
**Expected behavior**
Read and write a file without errors

**Screenshots**

> pyntcloud\io\ply.py:260: FutureWarning: Series.__getitem__ treating keys as positions is deprecated. In a future version, integer keys will always be treated as labels (consistent with DataFrame behavior). To access a value by position, use `ser.iloc[pos]`

**Desktop (please complete the following information):**
- OS: Windows 10 / python 3.10 / pandas 2.1.0
- Version: master branch commit