Fix broken link to the license
:target: https://anaconda.org/conda-forge/umap-learn
:alt: Downloads from conda-forge
.. image:: https://img.shields.io/pypi/l/umap-learn.svg
- :target: https://github.com/lmcinnes/umap/blob/master/LICENSE
+ :target: https://github.com/lmcinnes/umap/blob/master/LICENSE.txt
:alt: License
.. image:: https://travis-ci.org/lmcinnes/umap.svg
:target: https://travis-ci.org/lmcinnes/umap
