Parse correct AST attribute for version

Earlier development versions of Python 3.7 added the docstring field to
AST nodes.  This was later reverted in Python 3.7.0b5.

https://bugs.python.org/issue29463
python/cpython#7121

setup.py

@@ -3,18 +3,14 @@
 from setuptools import setup, find_packages
 
 import ast
-import sys
 
 __AUTHOR__ = 'David Halter'
 __AUTHOR_EMAIL__ = 'davidhalter88@gmail.com'
 
 # Get the version from within jedi. It's defined in exactly one place now.
 with open('jedi/__init__.py') as f:
     tree = ast.parse(f.read())
-if sys.version_info > (3, 7):
-    version = tree.body[0].value.s
-else:
-    version = tree.body[1].value.s
+version = tree.body[1].value.s
 
 readme = open('README.rst').read() + '\n\n' + open('CHANGELOG.rst').read()
 with open('requirements.txt') as f: