Support multiple merge commits while merged PRs collecting
Support multiple merge commits while merged PRs collecting

Bors can merge several PRs with one merge commit like https://github.com/intellij-rust/intellij-rust/commit/2301577ec5edb37612874480fea42d9b731117ac
These changes allow to correctly process the corresponding commit messages

intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io