Compile fails if there is a word import in comments

[visvirial]

If there is a comment or something which contains the string import, ./utils/stripper.js considers it as a module imports, and outputs a wrong JS string.

• Try adding a comment // This will import mylibrary. to ./__test__/echoworker.worker.js somewhere. This will throw a SyntaxError.
• The importRe regular expression in ./utils/stripper.js should be sophisticated, and / or some syntax interpretation should be applied.

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The fix should pass this test: https://github.com/visvirial/workerloader-jest-transformer/blob/import-comment/__test__/import_in_comments_ts.worker.ts

Related: #4