Disallow broken apipkg v2.1.0 under Python 3.4

Ref: pytest-dev/apipkg#29

Author: webknjaz

setup.cfg

@@ -149,6 +149,12 @@ testing =
   # of the control flow:
   pypytools
 
+  # NOTE: `apipkg` has broken the support of Python 3.4, seemingly
+  # NOTE: accidentally. It's a transitive dependency for us, through
+  # NOTE: `pytest-xdist` -> `execnet`.
+  # Ref: https://github.com/pytest-dev/apipkg/issues/29
+  apipkg != 2.1.0; python_version == "3.4"
+
 [options.entry_points]
 console_scripts =
   cheroot = cheroot.cli:main