adjust HAS_IMPORT regex

[manmen-mi]

fix #1060

match RegExp HAS_IMPORT with fileMayBeTailwindRelated()

---

let HAS_IMPORT = /@import\s*('[^']+'|"[^"]+");/
let HAS_IMPORT = /@import\s*['"]/ // from fileMayBeTailwindRelated()

It seemed like the regex only accepted @import '~~~';, so @import '~~~' layer(xxx); did not match.
Therefore, I loosened the regex of HAS_IMPORT a bit so that it would match the other parts.

_{translated from japanese}

[thecrypticace]

oops… lol. Thanks for the PR and the tests 💯