Update `uglifier` to improve security

Created by: gracewashere

Based on the recommendations of bundler-audit:

ruby-advisory-db: 227 advisories
Name: uglifier
Version: 2.7.0
Advisory: OSVDB-126747
Criticality: Unknown
URL: https://github.com/mishoo/UglifyJS2/issues/751
Title: uglifier incorrectly handles non-boolean comparisons during
minification
Solution: upgrade to >= 2.7.2

Unpatched versions found!