Update meteor to 1.8.1

[mrsimpson]

This is a cherry pick of a0d8658 which is included in Rocket.Chat 2.1 This not only brings the latest Meteor release, but also adapts CircleCI so that memory issues during build should not happen anymore

Update Meteor to 1.8.1 (#15358)

• Meteor update to 1.8.1

meteor update meteor update --all-packages

• Remove deprecated rocketchat:monitoring package

• Fix calling WebAppInternals.staticFilesMiddleware new signature

• Update Node version to 8.15

• Clear main files to cache some build files

• Meteor npm install

Closes #ISSUE_NUMBER

[mrsimpson]

@jschirrmacher the commit I cherry-picked unfortunately contained dependencies: GraphQL-support in the package-dependencies was removed with the same commit, but not dependent files.

Thus, I had to removed this in separate commits.