string_methods.cpp does not support ChaiScript 6+

[suratovvlad]

Function void vector_type(const std::string &type, Module& m) now accepts second parameter and returns nothing.
However you have following code:

  // Add the string_methods module.
  auto stringmethods = chaiscript::extras::string_methods::bootstrap();
  chai.add(chaiscript::bootstrap::standard_library::vector_type<std::vector<std::string>>("StringVector"));
  chai.add(stringmethods);