Update pylint from 2.5.3 to 2.6.0 (#57)

Author: pyup-bot

doc/sphinx/requirements.txt

@@ -40,7 +40,7 @@ ptyprocess==0.6.0
 py==1.9.0
 pycodestyle==2.6.0
 pygments==2.6.1
-pylint==2.5.3
+pylint==2.6.0
 pyparsing==3.0.0a2
 pyshark==0.4.2.11
 pysocks==1.7.1