Merge branch 'patch-4' into 'master'

Update textbook.es.md

See merge request m3p2/courses!6
1 job from master in 4 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Deploy
failed #453
deploy

00:00:04

 
Name Stage Failure
failed
deploy Deploy There has been a runner system failure, please try again
Running with gitlab-runner 11.8.0 (4745a6f3)
on 91a83f0bc80d _dMzKXrj
Using Docker executor with image appropriate/curl:latest ...
Pulling docker image appropriate/curl:latest ...
Using docker image sha256:d37e1f717dc01df3a838955d29a149c569352c0991b1d7cf11b4ebca8c6c7f55 for appropriate/curl:latest ...
ERROR: Job failed (system failure): Error response from daemon: failed to start shim: exec: "docker-containerd-shim": executable file not found in $PATH: unknown (executor_docker.go:1018:0s)