Docs: fix formula typo in documentation of the gauss decay in function_score
Docs: fix formula typo in documentation of the gauss decay in function_score

closes #7506

aparo/elasticsearch,aparo/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch