Merge pull request #1468 from sopel-irc/1461-dnspython-versions

Get specific about dnspython requirement

Author: dgw

requirements.txt

@@ -7,4 +7,6 @@ ipython<6.0; python_version < '3.3'
 ipython>=6.0,<7.0; python_version >= '3.3' and python_version < '3.5'
 ipython>=7.0,<8.0; python_version >= '3.5'
 requests>=2.0.0,<3.0.0
-dnspython
+dnspython<2.0; python_version >= '2.7' and python_version < '3.0'
+dnspython<1.16.0; python_version == '3.3'
+dnspython<3.0; python_version >= '3.4'