Handle verbose logs for constant program arguments

[abumq]

When program looks like:

int main(int argc, const char** argv) {
  _START_EASYLOGGINGPP(argc, argv)
 ...
}

Compiler has error that says invalid conversion from const char** to char**

Works for:

int main(int argc, char** argv) {
  _START_EASYLOGGINGPP(argc, argv)
 ...
}