Decaptcha

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* bump tensorflow to 1.15.2

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* refactor & rename tests
* Patch security vulnerability: bump tensorflow==1.15.0
* Add dev-requirements, update travis install
* sort imports
* Remove python 3.5, 3.5-dev, & 3.7 from travis build
* Add unittest for semver

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* Patch security vulnerability: pin pillow>=6.2.0
* Move requirements.in to setup.py
* Pin tensorflow==1.14.0
* Use __version__ in version.py

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* Patch false-positive collisions for 3x3 grid
* Replace pytesseract (GPL-3) w/ tesserocr (MIT)
* Add test for reset() method
* Optimize wait time for regenerated cells

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* Add initial_state=OpenGround() as default argument in NotARobot()

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* Use parse_requirements for install_requires in setup.py