Bump astor from 0.7.1 to 0.8.0

[dependabot-preview]

Bumps astor from 0.7.1 to 0.8.0.

Changelog

Sourced from astor's changelog.

0.8.0 - 2019-05-19

New features

• Support ast.Constant nodes being emitted by Python 3.8 (and initially created in Python 3.6). (Reported and fixed by Chris Rink in Issue 120 and PR 121.)
• Support Python 3.8's assignment expressions. (Reported and fixed by Kodi Arfer in Issue 126 and PR 134.)
• Support Python 3.8's f-string debugging syntax. (Reported and fixed by Batuhan Taskaya in Issue 138 and PR 139.)
• astor.to_source now has a source_generator_class parameter to customize source code generation. (Reported and fixed by matham in Issue 113 and PR 114.)
• The ~SourceGenerator class can now be imported from the astor package directly. Previously, the astor.code_gen submodule was needed to be imported.
• Support Python 3.8's positional only arguments. See 570 for more details. (Reported and fixed by Batuhan Taskaya in Issue 142 and PR 143.)

Bug fixes

• Fix string parsing when there is a newline inside an f-string. (Reported by Adam Cécile in Issue 119 and fixed by Felix Yan in PR 123.)
• Fixed code generation with escaped braces in f-strings. (Reported by Felix Yan in Issue 124 and fixed by Kodi Arfer in PR 125.)
• Fixed code generation with attributes of integer literals, and with u-prefixed string literals. (Fixed by Kodi Arfer in PR 133.)
• Fixed code generation with very large integers. (Reported by Adam Kucz in Issue 127 and fixed by Kodi Arfer in PR 130.)
• Fixed astor.tree_walk.TreeWalk when attempting to access attributes created by Python's type system (such as __dict__ and __weakref__) (Reported and fixed by esupoff in Issue 136 and PR 137.)

Commits

• 3a7607e Use twine when making test releases
• cb0032b Prepare for 0.8
• 14224f8 Remove Python 2.6 from trove classifiers
• 3d57876 Remove deprecated register command
• b958be1 Add support for PEP 570 (positional-only arguments) (#143)
• cdedca5 Allow specifying the generator class (#114)
• 1f35741 Integrate flake8 and coverage.py with tox (#141)
• ea4d9da Run tests under nose in python setup.py test
• c5d5b3c Fix TypeError when accessing TreeWalk().dict (#137)
• 70b5924 Add support for f-string debugging syntax (#139)
• Additional commits viewable in compare view

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[coveralls]

Pull Request Test Coverage Report for Build 1256

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1254:	0.0%
Covered Lines:	2596
Relevant Lines:	2596

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1256

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1254:	0.0%
Covered Lines:	2596
Relevant Lines:	2596

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💛 - Coveralls