Include "clientversion.h" in rpc/masternode.cpp (#1979)

Otherwise it fails to compile when the wallet is disabled at compile time

Author: codablock

src/rpc/masternode.cpp

@@ -4,6 +4,7 @@
 
 #include "activemasternode.h"
 #include "base58.h"
+#include "clientversion.h"
 #include "init.h"
 #include "netbase.h"
 #include "validation.h"