modified executeCommand function dir

Author: dixyushi

devon4j-migrate/index.asciidoc

@@ -31,7 +31,8 @@ Execute below command for project migration from an older version to the latest
 [step]
 == Execute Migrate Command
 --
-executeCommand("devon java migrate", "devon java migrate", {"dir":"devonfw/workspaces/main"})
+executeCommand("cd devonfw/workspaces/main", "cd devonfw/workspaces/main")
+executeCommand("devon java migrate", "devon java migrate")
 --
 You will see the message similar to the one below, if project migrated successfully.
 `Successfully applied 4 migrations to migrate project from version devon4j:2020.08.001 to devon4j:2021.04.002.`