Change Maps.newHashMap() to Maps.<String, Object>newHashMap()

Caused by elastic/elasticsearch#9992 (comment)

Author: dadoonet

src/main/java/org/elasticsearch/river/couchdb/CouchdbRiver.java

@@ -143,7 +143,7 @@ public CouchdbRiver(RiverName riverName, RiverSettings settings, @RiverIndexName
                 }
 
                 script = scriptService.executable(scriptType, couchSettings.get("script").toString(),
-                        ScriptService.ScriptType.INLINE, Maps.newHashMap());
+                        ScriptService.ScriptType.INLINE, Maps.<String, Object>newHashMap());
             } else {
                 script = null;
             }