[MetricsBot] Fix env variable name in config

pica-metrics-bot/config.json

@@ -27,8 +27,8 @@
     "wekan" : [
       {
         "url" : "https://kanban.picasoft.net",
-        "user" : "KANBAN_USER",
-        "password" : "KANBAN_PASSWORD",
+        "user" : "WEKAN_USER",
+        "password" : "WEKAN_PASSWORD",
         "name" : "kanban.picasoft.net"
       }
     ]