fix ios build

<thread> std include was missing to build on ios.

Change-Id: I8da9dd25e41d67ca3fa7343e487e2b0a94d93843
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>

src/sip/sipaccount.cpp

@@ -71,6 +71,7 @@
 #include <memory>
 #include <sstream>
 #include <cstdlib>
+#include <thread>
 
 #ifdef _WIN32
 #include <lmcons.h>