Fix prototype for main.

A typo in 297d7c06c4 meant main had the
wrong prototype on non-Windows systems, breaking the build.

src/wx/wxvbam.cpp

@@ -76,7 +76,7 @@ int WinMain(HINSTANCE hInstance,
 
 #else  // __WXMSW__
 
-int main(int argc, char* argv) {
+int main(int argc, char** argv) {
     // Set up logging.
 #ifdef DEBUG
     wxLog::SetLogLevel(wxLOG_Trace);