Travis + dependency updates

[JayH5]

Travis:

• Test with latest PyPy and PyPy3
• Test in dist: trusty, don't test on precise
• Add a job to build development Docker images
• Cleanup, rearrange

Code:

• Require newer treq version to avoid Twisted 17.1.0 compatibility issue
• Remove klein pin
• Require newer acme version, use functionality to get acme error code
• Require tls extras for Twisted.. apparently we need to do this

[codecov[bot]]

Codecov Report

Merging #95 into develop will decrease coverage by <.01%. The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop      #95      +/-   ##
===========================================
- Coverage    99.77%   99.77%   -0.01%     
===========================================
  Files           18       18              
  Lines         1747     1746       -1     
===========================================
- Hits          1743     1742       -1     
  Misses           4        4

Impacted Files	Coverage Δ
marathon_acme/service.py	100% <100%> (ø)	:arrow_up:

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