I am way late to this ball game, but I have to raise a point that I don't think anyone else has mentioned. Markdown behaves this way for a specific reason:
> Readability, however, is emphasized above all else. A Markdown-formatted document should be publishable as-is, as plain text, without looking like it ’ s been marked up with tags or formatting instructions. Source: Markdown Philosophy
In other words, Markdown is designed to be equally nicely formatted both as a text document and as an HTML document. That is the reason behind the line break behavior. Markdown documents read nicely as text documents because the author can control the text display without having to depend on the word-wrapping behavior of the editor. This is a feature and by design, not lazy programming as some have suggested.
I, for one, dislike GitHub for making the change they did, because now I have to make a choice between a Markdown document that looks nicely on GitHub and one that looks nicely to someone reading it in a terminal window.
github 确实是 1 次回车换行，你试试https://github.com/vuejs/vue/issues/new