[ABIDE] Documentation : Fix message when the form is valid

[ydrant]

Before submitting a pull request, make sure it's targeting the right branch:

• For documentation fixes, use master.
• For bug fixes, use develop.
• For new features, use the branch for the next minor version, which will be formatted v6.x.

If you're fixing a JavaScript issue, it would help to create a new test case under the folder test/visual/ that recreates the issue and show's that it's been fixed. Run npm test to compile the testing folder.

Happy coding! :)

Now display a correct message on the event "formvalid.zf.abide"