v154539-stable: Merge pull request #1665 from DFE-Digital/maintenance/upgrade-mimemagic

Changes:

• 118ee9b Merge pull request #1665 from DFE-Digital/maintenance/upgrade-mimemagic
• ce2ca64 Upgrade to mimemagic 0.3.9
• 6a5001c Upgrade to mimemagic 0.3.7
• 6b4a4dd Merge pull request #1663 from DFE-Digital/devops/use-build-cache-on-master-till-mimemagic-is-resolved
• ff210a7 Use cached builds on master as a stopgap fix
• 18d1366 Merge pull request #1662 from DFE-Digital/devops/only-run-js-specs-on-chrome
• 7d2e501 Only run chrome with javascript cucumber specs

This list of changes was auto generated.