doc: improve style guide text

* Specify that personal pronouns are OK in colloquial documentation
  rather than just pronouns. Pronouns are OK in all documentation. (For
  example, "it" is a pronoun and is acceptable in all types of
  documentation.) Specify "personal pronouns" for clarity.
* more colloquial -> colloquial
* like -> such as
* Remove "mass nouns" as no mass nouns are given as examples. Plural
  nouns seems to be what was meant, so use that instead.
* Repeat "gender-neutral" to make it clear that it refers to both terms
  and not merely the first term it appears before.
* Remove "non-comprehensive examples". Examples are, by definition,
  non-comprehensive. No need to announce that the examples are examples.
  It is obvious.

PR-URL: https://github.com/nodejs/node/pull/19269


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>