Merge pull request #7058 from docker/dependabot/pip/idna-2.8

Bump idna from 2.5 to 2.8

requirements.txt

@@ -10,7 +10,7 @@ dockerpty==0.4.1
 docopt==0.6.2
 enum34==1.1.6; python_version < '3.4'
 functools32==3.2.3.post2; python_version < '3.2'
-idna==2.5
+idna==2.8
 ipaddress==1.0.18
 jsonschema==3.0.1
 paramiko==2.6.0