running register from command line, `--executor X` results in: `ERROR: Invalid executor specified`

Summary

When trying to register a running using Docker-based gitlab-runner command docker exec -it runner-name gitlab-runner register and using the --executor tag, no value works, all values return ERROR: Invalid executor specified

Steps to reproduce

$ docker run -d \
	--name ci01 \
gitlab/gitlab-runner

$ docker exec -it ci01 gitlab-runner register -n \
--name my-runner \
--url http://myurl \
--registration-token {{TOKEN}} \
--tag-list asdf,qwerty \
--run-untagged true \
--executor shell

Actual behavior

returns error ERROR: Invalid executor specified

If you run it in interactive mode without -n it prompts you for the executor, and if you type in any of them, it finishes successfully

Expected behavior

Should not require manual input from user to enter appropriate executor

Relevant logs and/or screenshots

$ docker exec -it ci01 gitlab-runner register -n \
→ --name my-runner \
→ --url http://gitlab \
→ --registration-token 3GuiTt5Hc-c-yfogsKUM \
→ --tag-list asdf,qwerty \
→ --run-untagged true \
→ --executor "kubernetes"
Running in system-mode.

Registering runner... succeeded                     runner=3GuiTt5H
PANIC: Invalid executor specified
Deleting runner... succeeded                        runner=d7eb4677

Environment description

Docker for Mac

$ docker info
Containers: 2
 Running: 2
 Paused: 0
 Stopped: 0
Images: 15
Server Version: 1.13.1
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host ipvlan macvlan null overlay
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: aa8187dbd3b7ad67d8e5e3a15115d3eef43a7ed1
runc version: 9df8b306d01f59d3a8029be411de015b7304dd8f
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.8-moby
Operating System: Alpine Linux v3.5
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 1.952 GiB
Name: moby
ID: NTNS:3VVW:TM6P:3XQT:FXYA:6UM3:Q4S6:UTYY:RWIR:QE6D:7MPZ:BOMF
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 45
 Goroutines: 47
 System Time: 2017-03-02T20:28:37.631874887Z
 EventsListeners: 1
No Proxy: *.local, 169.254/16
Registry: https://index.docker.io/v1/
Experimental: true
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

Used GitLab Runner version

$ docker exec ci01 gitlab-runner --version
Version:      1.11.0
Git revision: 33af656
Git branch:   1-11-stable
GO version:   go1.7.5
Built:        Wed, 22 Feb 2017 15:57:56 +0000
OS/Arch:      linux/amd64