Quick patch release to address
Also updated the dynamic-import test app to Meteor 188.8.131.52.
Cherry-picking this change from the release-1.7.1 branch, where it has been well-validated by our beta testers. Fixes #9940.
…les. According to the plan described in #10134, whereas we had to pin these versions to exactly 7.0.0-beta.55 for Meteor 184.108.40.206, we must now require at least 7.0.0-beta.56 for Meteor 1.7.1, since other @babel/... packages used by babel-compiler and meteor-babel are currently at beta.56.