docs: fix 404 url
Fix 404 url in deps/acorn/README.md.
Original URL is 404, It should be https://babeljs.io/blog/2015/07/07/react-on-es6-plus
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines