Make all year-based hashtags evergreen (eliminate manual year update)

[obscurerichard]

@jrenaut did a fabulous job in #70 of updating the coffee ride to use a dynamic year in the web page and hash tag. We need to ferret out other places in the code base

https://freezingsaddles.org/pointless/dirtybiker

It looks like the only ones left are in the leaderboards/ directory, which might prove more of a challenge since these are templated differently:

$  grep -rIi 2018 leaderboards/*
leaderboards/dirtybiker.yml:description: Number of days with at least 1 off-road ride (#fs2018dirtybiker).
leaderboards/dirtybiker.yml:url: http://bikearlingtonforum.com/showthread.php?12874-fs2018dirtybiker-Pointless-Prize-Mountain-for-Dirt-Miles-for-Freezing-Saddles-2018
leaderboards/dirtybiker.yml:                  where R.name like '%#fs2018dirtybiker%'
leaderboards/opmdays.yml:  where date(R.start_date) in ('2018-01-26')

I'll update these manually to 2019 for now, this issue is for a permanent fix.