[DM-4106] Add credential caching to reduce GitHub API calls.
[DM-4106] Add credential caching to reduce GitHub API calls.

    * Use redis + scrypt to safely cache username + password to reduce
      the number of GitHub API calls.

	modified:   git-lfs-s3-server.rb

lsst-sqre/git-lfs-s3-server,lsst-sqre/git-lfs-s3-server