Update setup.cfg in preparation for release.

Author: dihm

setup.cfg

@@ -18,6 +18,7 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [options]
 zip_safe = False
@@ -29,7 +30,7 @@ install_requires =
   h5py>=2.9
   numpy>=1.15
   packaging>=20.4
-  pyqtgraph>=0.11.0rc0
+  pyqtgraph>=0.11.0
   qtutils>=2.2.3
   scipy
   setuptools_scm>=4.1.0