Revert "chore(deps): update dependency lerna to v3.15.0 (#2810)" and …

…pin.

In the same spirit as 840e2a7, this reverts
commit adde690 which Renovate re-upgraded
in #2810.

Therefore, this commit also puts a restriction within Renovate's
configuration to prevent further upgrades.  Unfortunately, this means we're
stuck at this version of Lerna until we get time to make a reproduction for
the issue I logged when this first cropped up in
lerna/lerna#2100, but I haven't yet found the
cycles to make that happen.

I guess our repository is a reliable reproduction, right now!