see commit hash
$ ruby path/to/beefdad.rb beefdad
Searching for a timestamp so the current commit hash begins with beefdad: done!
To change the commit's hash to beefdad5edd78de6f8beefb241acb3f88dff6e29, run the following command:
GIT_COMMITTER_DATE="1486240746 -0500" git commit --amend --no-edit --date "1405879324 -0400"