Allow running with Python 3.6 again

We test internally on older systems that have
Python 3.6, so we know the code still works there.

Author: benmwebb

python/saliweb/backend/__init__.py

@@ -23,8 +23,8 @@
 
 
 # Version check
-if sys.version_info[0:2] < (3, 7):
-    raise ImportError("This module requires Python 3.7 or later")
+if sys.version_info[0:2] < (3, 6):
+    raise ImportError("This module requires Python 3.6 or later")
 
 
 class InvalidStateError(Exception):