Update 'power-plants.json'

Query 'relation' elements with 'power' key and 'plant' tag or 'station' tag:

(node[power=plant];
node[power=station];
way[power=plant];
way[power=station];
relation[power=plant];
relation[power=station];)

Example:

Relation: Centrale hydroélectrique de Veytaux 1 (7251087).
See https://www.openstreetmap.org/relation/7251087#map=13/46.4175/6.9874.

power-plants.json

@@ -10,7 +10,9 @@
             "(node[power=plant];",
             "node[power=station];",
             "way[power=plant];",
-            "way[power=station];)"
+            "way[power=station];",
+            "relation[power=plant];",
+            "relation[power=station];)"
         ]
     }
 }