Modernize: Use "default" for destructors and copy constructors (#751)

src/parser.cpp

@@ -15,7 +15,7 @@ Parser::Parser() : m_pScanner{}, m_pDirectives{} {}
 
 Parser::Parser(std::istream& in) : Parser() { Load(in); }
 
-Parser::~Parser() {}
+Parser::~Parser() = default;
 
 Parser::operator bool() const {
   return m_pScanner.get() && !m_pScanner->empty();