fix: change keyword plugin and import regexp

[iChenLei]

Try to fix #3660

We discovered that the regex used for import and plugin have a ? at the end of them, which means @plugi and @impor work as well as @plugin and @import.
These are defined here: https://github.com/less/less.js/blob/master/packages/less/src/less/parser/parser.js#L1687 and https://github.com/less/less.js/blob/master/packages/less/src/less/parser/parser.js#L1847.
This doesn't look like an intentional decision and more of a regex mistake. See here for example inputs: https://regex101.com/r/NUw7E2/2
Is this correct? --from @edhgoose

less.js/packages/less/src/less/parser/parser.js

Line 1687 in a4b6c85

const dir = parserInput.$re(/^@import?\s+/);

less.js/packages/less/src/less/parser/parser.js

Line 1847 in a4b6c85

const dir = parserInput.$re(/^@plugin?\s+/);

ready for code review, cc @matthew-dean . btw, i add .DS_Store into .gitignore

• code complete
• unit test

[edhgoose]

This looks correct to me - thank you.

I'm not sure if a test already exists for this, but perhaps another test to confirm that the plugin and import must be proceeded by the @ symbol and followed by a space might be a good idea? I don't think I can see tests that prove this?

Same for perhaps ensuring that they're at the beginning of a line too? This may be going too far, but might help if anyone changes these regexes in the future.