Source the Maps

[kylerwsm]

Problem

Modified webpack to generate sourcemaps while bundling, and implemented the uploading of sourcemaps to Sentry on production and staging builds.

Edit: Updated README.md with new environment variables.

Closes #28.

Solution

On gogovsg, the build is done twice, once on Travis and another one via the dockerfile. This solution only builds and upload sourcemaps while building on Travis.

The workflow is webpack will check whether all the required environment variables for Sentry sourcemap upload are defined. If they are defined, webpack will include an additional plugin, that will help us to upload the sourcemap, to its list of plugins. I have done this as the build will fail if the Sentry webpack plugin is included without all the relevant environment variables defined.

I also added logs that will be printed during builds for our own sanity checks.

Improvements:

• Code formatting by eslint, removed redundant newlines.
• Disable Travis notifications for subsequent successful builds.

Deploy Notes

New environment variables:

The following environment variables have been defined on Travis:

• SENTRY_AUTH_TOKEN: (Secret) To get permissions to write the source maps.
• SENTRY_DNS: The relevant Sentry DNS.
• SENTRY_ORG: Our Sentry organisation name.
• SENTRY_PROJECT: The relevant Sentry project (production, staging, etc.).
• SENTRY_URL: The Sentry url.

New dev dependencies:

• @sentry/webpack-plugin : The relevant package that helps us to upload our webpack sourcemaps to Sentry.

[liangyuanruo]

Code looks good. Have you tested? Also please rebase (or start working on this repo itself instead of using a fork)

[kylerwsm]

Branch seems to be up to date already. Added new environment variables to README.md.