Switch regex option multiline on

And use a begin-of-line anchor in the pattern, which makes it faster and
more specific.

src/main.cpp

@@ -57,7 +57,7 @@ int main(int argc, char* argv[]) {
         }
         sc::requester req;
         std::string text {req.get("https://gitlab.com/gitlab-org/gitlab-foss/-/raw/master/CHANGELOG.md")};
-        std::regex pat {R"(##\s+(\d+\.\d+\.\d+)\s+\((\d+-\d+-\d+))"};
+        std::regex pat {R"(^##\s+(\d+\.\d+\.\d+)\s+\((\d+-\d+-\d+))", std::regex::multiline};
         std::sregex_iterator beg {text.begin(), text.end(), pat};
         std::sregex_iterator end {};
         for (std::sregex_iterator i = beg; i != end; ++i) {