minor #6747 Correcting reference to isSuccessful method for Process (aedmonds)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #6747).

Discussion
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Correcting reference to `isSuccessful` method for Process

Stumbled across this misnamed method when doing some copying and pasting. "Successful" vs. "successfull" always gets me too.

Commits
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7dca444 Correcting reference to `isSuccessful` method for Process

Author: xabbuh

components/console/helpers/debug_formatter.rst

@@ -125,7 +125,7 @@ notify this to the users::
         $debugFormatter->stop(
             spl_object_hash($process),
             'Some command description',
-            $process->isSuccessfull()
+            $process->isSuccessful()
         )
     );