python37Packages.pex: 1.6.2 -> 1.6.3

Semi-automatic update generated by
https://github.com/ryantm/nixpkgs-update tools. This update was made
based on information from
https://repology.org/metapackage/python3.7-pex/versions

(cherry picked from commit 5e074ac3e769968a73a1f0305ae5bd105130cee1)