Fix webpack compilation error when pushing to heroku

[diego-suarez]

trafficstars

Board:

N/A

---

Description:

Pushing to Heroku was throwing errors related to webpack. Updating webpacker package version fixes the problem. Heroku logs before:

Compilation failed:
       Invalid options object. Compression Plugin has been initialized using an options object that does not match the API schema.
        - options has an unknown property 'cache'. These properties are valid:
          object { test?, include?, exclude?, algorithm?, compressionOptions?, threshold?, minRatio?, deleteOriginalAssets?, filename? }
       ValidationError: Invalid options object. Compression Plugin has been initialized using an options object that does not match the API schema.
           at validate (/tmp/build_00139f41/node_modules/compression-webpack-plugin/node_modules/schema-utils/dist/validate.js:104:11)
           at new CompressionPlugin (/tmp/build_00139f41/node_modules/compression-webpack-plugin/dist/index.js:26:31)
           at new module.exports (/tmp/build_00139f41/node_modules/@rails/webpacker/package/environments/production.js:13:7)
           at createEnvironment (/tmp/build_00139f41/node_modules/@rails/webpacker/package/index.js:15:10)
           at Object.<anonymous> (/tmp/build_00139f41/node_modules/@rails/webpacker/package/index.js:21:16)
           at Module._compile (/tmp/build_00139f41/node_modules/v8-compile-cache/v8-compile-cache.js:194:30)
           at Object.Module._extensions..js (internal/modules/cjs/loader.js:1176:10)
           at Module.load (internal/modules/cjs/loader.js:1000:32)
           ....

[santib]

@diego-suarez would you mind rebasing and merging? Thanks 🙌

[megatux]

Just in case you want to move fordward with this fix, I have rebased this branch with master in my forked repo