refactor: update export_plugins() to work with asdf v0.16

[egriff89]

asdf was recently updated to 0.16 and includes a multitude of breaking changes, some of which include the removal of hyphenated commands. This fixes the export_plugins() function to use asdf plugin list instead of asdf plugin-list to restore the intended functionality instead of the broken help text shown below.

Before:

$ asdf-plugin-manager.sh export
version:     0.16.0-arch                      
MANAGE       PLUGINS                          
asdf         plugin                           <name>
add          Git                              
specifying   name                             
asdf         plugin                           [--urls]
git          and                              
asdf         plugin                           all
repository   URLs                             
asdf         plugin                           <name>
asdf         plugin                           <name>
default      or                               
asdf         plugin                           --all
default                                       
MANAGE       TOOLS                            
asdf         current                          current
used         all                              
asdf         current                          Display
used         package                          
asdf         help                             [<version>]
asdf         install                          all
in           .tool-versions                   
asdf         install                          Install
specified    the                              
asdf         install                          <version>
asdf         install                          latest[:<version>]
package,     with                             
install      latest                           
begins       the                              
asdf         latest                           [<version>]
asdf         latest                           Show
packages     if                               
asdf         list                             [version]
optionally   the                              
asdf         list                             <name>
optionally   the                              
asdf         set                              [-p]
the          directory,                       
directory.                                    
asdf         uninstall                        <version>
asdf         where                            [<version>]
or           version                          
asdf         which                            Display
UTILS                                         
asdf         exec                             [args...]
asdf         env                              [util]
environment  for                              
asdf         info                             OS,
asdf         version                          the
asdf         reshim                           <version>
asdf         shim-versions                    List
provide      command                          
RESOURCES                                     
GitHub:      https://github.com/asdf-vm/asdf  
Docs:        https://asdf-vm.com              
PLUGIN       direnv                           
asdf         _asdf_cached_envrc.bash          
asdf         envrc.bash                       
asdf         hook-asdf.bash                   
asdf         install.bash                     
asdf         local.bash                       
asdf         setup.bash                       
asdf         shell.bash                       
"Late        but                              
--           Rajinikanth 

After:

$ asdf-plugin-manager.sh export
direnv               https://github.com/asdf-community/asdf-direnv.git          951acd38bf9aa2258a00a5d87cc9d971fd344a60
pipx                 https://github.com/yozachar/asdf-pipx.git                  31db61862805766b456e8920c635c19872ac87a7