Remove completion command (#607)

* Remove `completion` command
* Bump cobra dependency for better zsh completion

`docker app completion` is not consistent with docker CLI
replaced by `--completion` flag (hidden)

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

Author: ndeloof

Gopkg.lock

@@ -388,31 +388,6 @@ Commands:
 Run 'docker app COMMAND --help' for more information on a command.
 ```
 
-## Shell completion
-
-### Bash
-
-Load the completion code for bash into the current shell:
-```console
-$ source <(docker app completion bash)
-```
-Set the completion code for bash to autoload on startup in your ~/.bashrc, ~/.profile or ~/.bash_profile:
-```console
-source <(docker app completion bash)
-```
-**Note**: `bash-completion` is needed.
-
-### Zsh
-
-Load the completion code for zsh into the current shell
-```console
-$ source <(docker app completion zsh)
-```
-Set the completion code for zsh to autoload on startup in your ~/.zshrc
-```console
-source <(docker app completion zsh)
-```
-
 ## Experimental
 
 Some commands are flagged as experimental and will remain in this state until

README.md

@@ -5,7 +5,6 @@ A tool to build and manage Docker Applications.
 
 Commands:
   bundle      Create a CNAB invocation image and `bundle.json` for the application
-  completion  Generates completion scripts for the specified shell (bash or zsh)
   init        Initialize Docker Application definition
   inspect     Shows metadata, parameters and a summary of the Compose file for a given application
   install     Install an application