package/mender-artifact: bump version to 3.4.0

package/mender-artifact: bump version to 3.4.0

Update the following license file hashes due to copyright year changes:
  - vendor/github.com/mendersoftware/mendertesting/LICENSE
  - vendor/github.com/davecgh/go-spew/LICENSE
  - vendor/github.com/stretchr/testify/LICENSE

Add hashes for the the following new files:
  - vendor/github.com/minio/sha256-simd/LICENSE
  - vendor/gopkg.in/yaml.v2/LICENSE
  - vendor/github.com/klauspost/compress/LICENSE
  - vendor/github.com/russross/blackfriday/v2/LICENSE.txt
  - vendor/github.com/klauspost/pgzip/LICENSE
  - vendor/github.com/cpuguy83/go-md2man/v2/LICENSE.md
  - vendor/github.com/shurcooL/sanitized_anchor_name/LICENSE

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>