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Merge pull request #33 from Typeform/master

Add CompositeGraph, ActiveThreadsOverTime and PerfmonCollector support
bump version
Change mock to double to make tests pass

Mock have been deprecated in new version of rspec
See compare here
https://github.com/rspec/rspec-mocks/compare/v3.0.0.beta1...v3.0.0.beta2
Commit ef4aa3b