Remove jeweler. Add tzinfo. Update gems.

Adding tzinfo to development deps was required, removed jeweller because it added a layer of complexity around the gemspec file of dubious benefit.

Travis can run our tests; there are 50 failures -- same 50 failures even if the two recent PRs I merged were reverted (so I don't need to beat up on those authors).

Will leave this PR open for comment for a day or two and then will merge.