web/boids.js: Code style fixes

Found with gjslint.
web/boids.js: Call initial tick with an argument.

tick() accepts a numerical timestamp as an argument, which is normally
supplied by the requestAnimationFrame() callback. By calling tick()
first with a numerical argument, we can avoid having to perform an
undefined check on every subsequent tick.
web/boids.js: Max speed is time-dependent

This fixes the min and max speed implementation by making it dependent
on the tick time.
particle-swarm: Max speed is time-dependent

This fixes the min and max speed implementation by making it dependent
on the tick time.

Same as:

  04b4611 web/boids.js: Max speed is time-dependent
particle-swarm: web: Better alignment comment