escala 1: Meteor 1.6.1.1 -> 1.8.3

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.

.meteor/.finished-upgraders

@@ -15,3 +15,5 @@ notices-for-facebook-graph-api-2
 1.4.1-add-shell-server-package
 1.4.3-split-account-service-packages
 1.5-add-dynamic-import-package
+1.7-split-underscore-from-meteor-base
+1.8.3-split-jquery-from-blaze