doc: fix line length in esm.md
https://github.com/nodejs/node/commit/f92df338321ac528747ea2374dd72d95bdd1059a#r38024608
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