Deis Dockerbuilder v2.6.0

v2.5.2 -> v2.6.0

Features

• 003e8dd Makefile: set docker build flags via environment variable

Refactors

• 7bb769f deploy.py: placate new flake8 linter checks

Fixes

• f14a6db Dockerfile: fix gunzip -f

Maintenance

• d6b188d dev_requirements: upgrade flake8 to 3.2.1
• 82f77c3 Dockerfile: update deis/base to v0.3.6