squash! Restrict pylint version to <2.5

Pylint 2.5 errors if the package being checked is not
installed. It is not clear whether this is an intentional
change or not, so we are temporarily avoiding this
version.

CHANGES.rst

@@ -25,7 +25,11 @@ Release History
 **Added**
 
 - Added support for new ``one_page`` option in ``nengo-sphinx-theme``. (`#101`_)
-- Add upper bound to pylint version. (`#103`_)
+
+**Changed**
+
+- Restrict pylint version to <2.5 due to issue when the package being checked
+  is not installed in the current environment. (`#103`_)
 
 .. _#101: https://github.com/nengo/nengo-bones/pull/101
 .. _#103: https://github.com/nengo/nengo-bones/pull/103