Fix some typos in the documentation

Status Job ID Name Coverage
  Test
failed #6229
test

00:00:05

 
Name Stage Failure
failed
test Test
Running with gitlab-runner 11.7.0 (8bb608ff)
on gitlab-ci-shared 3cef6525
Using Docker executor with image ai/test:go ...
Pulling docker image ai/test:go ...
ERROR: Job failed: Error response from daemon: pull access denied for ai/test, repository does not exist or may require 'docker login' (executor_docker.go:168:1s)