doc: fixup esm resolver spec formatting
This fixes up the formatting of the esm resolver spec in the docs, which is currently showing some markdown issues - https://nodejs.org/dist/latest-v12.x/docs/api/esm.html#esm_resolution_algorithm.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines