Fix issue with UMAP import

[xoubinha]

• Modify UMAP import.

Explanation:
When trying to import bertopic I was getting an AttributeError related to UMAP import, saying:
module umap has no attribute UMAP
I checked that I had the correct version of umap-learn but still it wasn't working. Changing the imports as in the PR solved the issue. 😊

[MaartenGr]

The changes that you propose are workarounds to the issues mentioned here and here. To understand whether the change is truly necessary, it is important that we understand why you are facing this issue. Did you have a previous version of umap installed together with umap-learn? That typically seems to be the issue as many install UMAP with pip install umap instead of pip install umap-learn. Also, did you try it out in a fresh environment?

[xoubinha]

I did it in a fresh environment, but it must have used already installed packages. I tried it again uninstalling everything and it did work.