Log Message:
ledger: update to 3.1.3.

## 3.1.3 (2019-03-31)

- Properly reject postings with a comment right after the flag (bug #1753)

- Make sorting order of lot information deterministic (bug #1747)

- Fix bug in tag value parsing (bug #1702)

- Remove the `org` command, which was always a hack to begin with (bug #1706)

- Provide Docker information in README

- Various small documentation improvements