Permanent writing into redis db

Hello,
if I ```redis-cli monitor``` my redis during running kue I see the folllowing output, nearly every second:
```
1540977629.033304 [0 127.0.0.1:37796] "set" "promotion:lock" "NVuOgNzuEeisVyMzkGbzew==" "PX" "2000" "NX"
1540977629.033685 [0 127.0.0.1:37796] "set" "activeJobsTTL:lock" "NVu1kNzuEeisVyMzkGbzew==" "PX" "2000" "NX"
1540977629.034601 [0 127.0.0.1:37790] "zrangebyscore" "q:jobs:delayed" "0" "1540977629034" "LIMIT" "0" "1000"
1540977629.034984 [0 127.0.0.1:37790] "zrangebyscore" "q:jobs:active" "100000" "1540977629034" "LIMIT" "0" "1000"
1540977629.035340 [0 127.0.0.1:37796] "evalsha" "8797e0a1d8a2721e3b17f21ae1236166a81be165" "1" "promotion:lock" "NVuOgNzuEeisVyMzkGbzew=="
1540977629.035477 [0 lua] "get" "promotion:lock"
1540977629.035523 [0 lua] "del" "promotion:lock"
1540977629.035742 [0 127.0.0.1:37796] "evalsha" "8797e0a1d8a2721e3b17f21ae1236166a81be165" "1" "activeJobsTTL:lock" "NVu1kNzuEeisVyMzkGbzew=="
1540977629.035851 [0 lua] "get" "activeJobsTTL:lock"
1540977629.035890 [0 lua] "del" "activeJobsTTL:lock"
```
This output also appears if there is no job in the queue. Is that how it's supposed to be?

Start by reproducing the reported output with redis-cli monitor while Kue runs both with and without jobs in the queue. Trace the promotion:lock and activeJobsTTL:lock operations shown in the Redis monitor output, and determine whether the repeated writes are expected behavior or an unintended change.

Written by the indexing model from the issue text.