Gitlab CI uses "Docker executor" instead of shell

This is my /etc/gitlab-runner/config.toml -

concurrent = 1
check_interval = 0

[[runners]]
name = “name”
url = “https://gitlab.com/ci”
token = “[tocken]”
executor = “shell”
[runners.cache]

But when I push to the repository it randomly runs docker instead of shell -

Running with gitlab-ci-multi-runner 1.10.4 (b32125f)
Using Docker executor with image ruby:2.1 …
Pulling docker image ruby:2.1 …

What I am doing wrong?
May be there is a way to specify shell executor in .gitlab-ci.yml?

And this is your only runner? / The only runner connected to your Gitlab instance?

Yes it is

I think you should configure your Gitlab project to only use your private runner. Go to your project settings: CI/CD pipelines settings and then:

• Enable the available specific runner listed under Availabe specific runnners
• Disable shared runners for your project

It seems your job is ran on a shared Gitlab.com runner.