fixes warning in pumap about compatibiltity of tf-probability package…

[lukaschoebel]

• removes unused function import + typo fix
• warning now includes potential compatibility issue and hints towards the official release page

See #691

[pep8speaks]

Hello @lukaschoebel! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file umap/parametric_umap.py:

Line 46:87: W291 trailing whitespace
Line 54:82: W291 trailing whitespace
Line 55:60: W291 trailing whitespace
Line 150:89: E501 line too long (89 > 88 characters)

[coveralls]

Coverage decreased (-0.003%) to 87.697% when pulling a2eb29b on lukaschoebel:tf-probability-warning into 0865ef1 on lmcinnes:master.

[timsainb]

Looks good to me! Thanks @lukaschoebel