Add postcode to the filtered parameters

This will prevent postcodes from ending up in the application logs.
Merge pull request #493 from alphagov/filter_postcodes

Add postcode to the filtered parameters
Increase the number of workers to 4 per box
Merge pull request #494 from alphagov/increase_workers

Increase the number of workers to 4 per box
Bump logstasher to 0.4.1

To get https://github.com/shadabahmed/logstasher/pull/17
Swap order of Gemfile source lines

To prefer gems from gemfury over rubygems.org in the case where a gem
exists on both.
Log GOVUK-Request-Id header
Pass GOVUK-Request-Id header on api interaction

https://github.com/alphagov/gds-api-adapters?#middleware-for-request-tracing
Merge pull request #496 from alphagov/pass-on-GOVUK-Request-Id-on-api-calls

Pass GOVUK-Request-Id header on api interaction
Merge pull request #495 from alphagov/log_request_id

Log GOVUK-Request-Id header
Revert "Swap order of Gemfile source lines"

This reverts commit 50283dd911950f9f72847cca753eac7ebb2087b4.

The search order is actually from last to first
Remove setting of slimmer campaign_notification header

This was removed from slimmer in alphagov/slimmer#54, and therefore this
will cause errors when slimmer is upgraded.
Merge pull request #497 from alphagov/remove_slimmer_campaign_notification

Remove setting of slimmer campaign_notification header
Bump slimmer to 3.25.0

To get GOVUK-Request-Id header passing
Merge pull request #498 from alphagov/bump_slimmer

Bump slimmer to 3.25.0
Merge branch 'master' into tax_disc_start_page