Allow pluggy >=1.0

Now that pluggy 1.0 has been released, we can allow pluggy 1.0 with new pytest versions.

Author: nicoddemus

setup.cfg

@@ -45,7 +45,7 @@ install_requires =
     attrs>=19.2.0
     iniconfig
     packaging
-    pluggy>=0.12,<1.0.0a1
+    pluggy>=0.12,<2.0
     py>=1.8.2
     tomli>=1.0.0
     atomicwrites>=1.0;sys_platform=="win32"