Lowercase the IPv4 and IPv6 attributes, because of there have a java style...

Lowercase the IPv4 and IPv6 attributes, because of there have a java style check that regulate the first letter must be lowercase.

apm-protocol/apm-ui-protocol/src/main/resources/ui-graphql/server-layer.graphqls

@@ -10,8 +10,8 @@ type AppServerInfo {
     os: String
     host: String
     pid: Int
-    IPv4: String
-    IPv6: String
+    ipv4: String
+    ipv6: String
 }
 
 type CPUTrend {