Fix regex.hh compilation

Repeat after me: I will not blindly push commits that I havent
compiled.

Fixes #990

src/regex.hh

@@ -20,7 +20,7 @@ struct regex_error : runtime_error
 using RegexBase = boost::basic_regex<wchar_t, boost::c_regex_traits<wchar_t>>;
 
 // Regex that keeps track of its string representation
-class Regex : RegexBase
+class Regex : public RegexBase
 {
 public:
     Regex() = default;