HPCC-10628 Fixed typo in EVENTEXTRA docs

Signed-off-by: JamesDeFabia <James.Defabia@LexisNexis.com>
Merge pull request #5315 from JamesDeFabia/10628_EVENTEXTRA_doc_typo

HPCC-10628 Fixed typo in EVENTEXTRA docs

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>