Update webpack, terser-webpack-plugin, compression-webpack-plugin

[pustovalov]

New versions of packages contain fixes: regular expressions Cross-Site Scripting (XSS) vulnerability
GHSA-h9rv-jmmf-4pgx

webpack changelog: webpack/webpack@b396d96

terser-webpack-plugin:
webpack-contrib/terser-webpack-plugin@b33ff1a
webpack-contrib/terser-webpack-plugin@0bc8435

compression-webpack-plugin:
webpack-contrib/compression-webpack-plugin@b7e65f2#diff-b9cfc7f2cdf78a7f4b91a753d10865a2R44

[pustovalov]

ran tests locally:

................................................................

Finished in 5.669394s, 11.2887 runs/s, 23.4593 assertions/s.
64 runs, 133 assertions, 0 failures, 0 errors, 0 skips

it looks like this setting for travis stopped working:
https://github.com/rails/webpacker/blob/master/.travis.yml#L9

$ gem install rubygems-update && update_rubygems
Fetching: rubygems-update-3.1.1.gem (100%)
Successfully installed rubygems-update-3.1.1
1 gem installed
  Successfully built RubyGem
  Name: bundler
  Version: 2.1.0
  File: bundler-2.1.0.gem
bundler's executable "bundle" conflicts with /home/travis/.rvm/rubies/ruby-2.3.8/bin/bundle
Overwrite the executable? [yN]  
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received
The build has been terminated