Trying to make CI pick up tkinter-gl by explicitly specifying version…

… number.

setup.py

@@ -514,7 +514,7 @@ def add(self, source_file, dependency_mod_time=0.0):
 
 install_requires = ['plink>=2.4.2', 'spherogram>=2.2', 'FXrays>=1.3',
                     'snappy_manifolds>=1.2', 'low_index>=1.2',
-                    'pypng', 'decorator', 'packaging', 'tkinter-gl']
+                    'pypng', 'decorator', 'packaging', 'tkinter-gl==1.0a2']
 try:
     import sage
 except ImportError: