use struct Config

Change-Id: I3c26a2e4be32899fe3f8eff5934b3ed148934512
diff --git a/include/connectionmanager.h b/include/connectionmanager.h
index 22f6aa0..2e8fb9e 100644
--- a/include/connectionmanager.h
+++ b/include/connectionmanager.h
@@ -86,7 +86,7 @@
 class ConnectionManager
 {
 public:
-    class Config;
+    struct Config;
 
     ConnectionManager(std::shared_ptr<Config> config_);
     ~ConnectionManager();