core: fix typo

1 job for master in 19 seconds (queued for 7 seconds)
Name Stage Failure
failed
build Build There has been a runner system failure, please try again
WARNING: Failed to pull image with policy "always": Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit (manager.go:205:1s)
ERROR: Preparation failed: failed to pull image "debian:sid" with specified policies [always]: Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit (manager.go:205:1s)
Will be retried in 3s ...
Using Docker executor with image debian:sid ...
Pulling docker image debian:sid ...
WARNING: Failed to pull image with policy "always": Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit (manager.go:205:1s)
ERROR: Preparation failed: failed to pull image "debian:sid" with specified policies [always]: Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit (manager.go:205:1s)
Will be retried in 3s ...
ERROR: Job failed (system failure): failed to pull image "debian:sid" with specified policies [always]: Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit (manager.go:205:1s)