Correctly check whether the time is in the past

[javitonino]

Previous code checked if the time was less than 1 second in the future, which produces incorrect results when the period between allowed requests is < 1 second (rate > 1/s).

Closes #12

[javitonino]

Test script:

require "redis"

r = Redis.new(port: 9000)
num_allowed = 0
num_blocked = 0

start = Time.now
begin
  1000.times do
    resp = r.call("CL.THROTTLE", "user#{start}", "10", "100", 1, 1)
    if resp[0] == 0
      num_allowed += 1
    else
      num_blocked += 1
      sleep 0.1
    end
  end
ensure
  elapsed = Time.now - start
  p "Allowed: #{num_allowed}"
  p "Blocked: #{num_blocked}"
  p "Elapsed: #{elapsed} s"
  p "Rate: #{num_allowed/elapsed}"
end

I expect a rate ~100 req/s (a bit higher, because of the initial burst).

Before this PR:

"Allowed: 466"
"Blocked: 34"
"Elapsed: 3.564658991 s"
"Rate: 130.72779224507875"

After this PR:

"Allowed: 366"
"Blocked: 35"
"Elapsed: 3.661400648 s"
"Rate: 99.96174556857729"

[brandur]

Wow, amazing work tracking this one down. Thanks @javitonino and all!

I'd forgotten that I'd written this, but looking at it now, I can't believe I didn't catch this at the time. It's quite a glaring hole in retrospect.