Changed the required version of pyflakes to one that supports ANNASSIGN (python annotated assignments, now used in the code)

 - Legacy-Id: 17982

Author: levkowetz

requirements.txt

@@ -47,7 +47,7 @@ pathlib2>=2.3.0
 Pillow>=3.0
 #pip==9.0.1			# Earlier pip has issues, 9.0.2 and 9.0.3, 10.0.0b1 leaves dross when down- and up-grading packages
 pyang>=1.7.2
-pyflakes>=0.9.2
+pyflakes>=1.5.0
 pyopenssl>=17.5.0		# Used by urllib3.contrib, which is used by PyQuery but not marked as a dependency
 pyquery>=1.3.0
 python-dateutil>=2.4