Print failures to stderr

Failure example:
    aerospace list-windows --unknow-flag

(cherry picked from commit 86c8ba8)

Sources/Cli/main.swift

@@ -43,8 +43,7 @@ if !isVersion {
  print(help)
  exit(0)
  case .failure(let e):
- print(e)
- exit(1)
+ prettyError(e)
  }
 }