Fixed wrong url and added quotes around “_source” in javadocs

Author: markharwood

client/rest-high-level/src/main/java/org/elasticsearch/client/RestHighLevelClient.java

@@ -728,8 +728,8 @@ public final void existsAsync(GetRequest getRequest, RequestOptions options, Act
     }
 
     /**
-     * Checks for the existence of a document with a _source field. Returns true if it exists, false otherwise.
-     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-get.html#_sourcel">Source exists API 
+     * Checks for the existence of a document with a "_source" field. Returns true if it exists, false otherwise.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-get.html#_source">Source exists API 
      * on elastic.co</a>
      * @param getRequest the request
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
@@ -741,8 +741,8 @@ public boolean existsSource(GetRequest getRequest, RequestOptions options) throw
     }     
 
     /**
-     * Asynchronously checks for the existence of a document with a _source field. Returns true if it exists, false otherwise.
-     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-get.html#_sourcel">Source exists API 
+     * Asynchronously checks for the existence of a document with a "_source" field. Returns true if it exists, false otherwise.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-get.html#_source">Source exists API 
      * on elastic.co</a>
      * @param getRequest the request
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized