[ML][DOCS] Fix doc error for forecast API
[ML][DOCS] Fix doc error for forecast API

Original commit: elastic/x-pack-elasticsearch@5156c4ff19d67e1f86f4b1cf03946ffe96de6b9e

strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,vroyer/elassandra