Empirically verified: 2.4 and 2.5 green against mongo:3.2 (npm-mongo 3.9.1); 2.6 bumps npm-mongo to 4.3.1 which refuses MongoDB < 3.6 (MongoCompatibilityError, wire version 4). Branch lands on Meteor 2.5.
meteor update --release 1.8.3 + Babel beta->stable fix. - Core packages bumped (meteor 1.9.3, ecmascript 0.13.2, mongo 1.7.0, npm-mongo 3.2.0 driver — still compatible with Mongo 3.2 server). - Fix boot failure 'Cannot find @babel/runtime/helpers/objectSpread2': upgraded @babel/runtime 7.0.0-beta.44 -> ^7.29.7 (stable 7.x; not 8.x). - underscore auto-added, fetch/modern-browsers added by the release. REST smoke test byte-identical to baseline. See UPGRADE.md.