Fix usage of boost in Elasticsearch hints

SELECT * FROM Document WHERE /*+ES: INDEX(dc:title.fulltext^5, dc:description.fulltext^2) */ ecm:fulltext = 'workspaces'

curl -XGET 'http://localhost:9200/nuxeo/doc/_search?pretty&search_type=dfs_query_then_fetch' -d '{
  "from" : 0,
  "size" : 20,
  "query" : {
    "simple_query_string" : {
      "query" : "workspaces",
      "fields" : [
        "dc:description.fulltext^2^1.0",
        "dc:title.fulltext^5^1.0"
      ],
      "analyzer" : "fulltext",
      "flags" : -1,
      "default_operator" : "and",
      "lenient" : false,
      "analyze_wildcard" : false,
      "boost" : 1.0
    }
  },
  "_source" : {
    "includes" : [
      "_id"
    ],
    "excludes" : [ ]
  }
}'