Aria2 warn message

[Ash258]

Message about installing using Aria2c (presented in 8c77bf7) should not be shown in scoop update <manifest || *>, when there is no update available or something other went wrong.

system32 $ scoop update *
Latest versions for all apps are installed! For more information try 'scoop status'
WARN  Scoop uses 'aria2c' for multi-connection downloads.
WARN  Should it cause issues, run 'scoop config aria2-enabled false' to disable it.

system32 $ scoop update firefox-developer
firefox-developer: nightly-20180726 (latest version)
Latest versions for all apps are installed! For more information try 'scoop status'
WARN  Scoop uses 'aria2c' for multi-connection downloads.
WARN  Should it cause issues, run 'scoop config aria2-enabled false' to disable it.

system32 $ scoop update foo
ERROR 'foo' isn't installed.
WARN  Scoop uses 'aria2c' for multi-connection downloads.
WARN  Should it cause issues, run 'scoop config aria2-enabled false' to disable it.

[se35710]

Also scoop config aria2-enabled true should disable the message all together.