Update release notes (rethinkdb#6909)

Regenerte web assets

Update NOTES.md for v2.3.7

Revert "Use pre-generated src/gen/web_assets.cc"

This reverts commit bd461da.

This is a cheap way to get bionic deb packaging working.  It would
be nice to remove the npm build dependency, but I guess we are not
there yet.

Merge tag 'v2.3.6' into v2.3.x-windows

RethinkDB 2.3.6

RethinkDB 2.3.6

RethinkDB 2.3.6-0RC2

Updating copyright years.

Merge branch 'v2.3.x' into v2.3.x-windows

RethinkDB 2.3.5