Bump github.com/docker/docker from 1.4.2-0.20200214221943-d8772509d1a2 to 26.1.0+incompatible in /tests/integration/functional

Bump github.com/docker/docker from 1.4.2-0.20200214221943-d8772509d1a2 to 26.1.0+incompatible in /tests/integration/functional #13