This enables us to remove the following patterns that required
a `rm -rf /var/cache/apk`:
- `apk update`
- `apk add --update`
- `apk add --update-cache`
Supported since alpine 3.3.
This updates vault to 0.5.3, and includes some optimizations:
- GO15VENDOREXPERIMENT is no longer needed, as
the Dockerfile uses Go 1.6+
- Added XC_OSARCH to prevent building all possible
OS/Arch combinations during build
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
