Change Python version guard in pybind11/__init__.py: pybind11 does not support Python < 3.7.

Author: rwgk

pybind11/__init__.py

@@ -1,7 +1,7 @@
 import sys
 
-if sys.version_info < (3, 6):  # noqa: UP036
-    msg = "pybind11 does not support Python < 3.6. 2.9 was the last release supporting Python 2.7 and 3.5."
+if sys.version_info < (3, 7):  # noqa: UP036
+    msg = "pybind11 does not support Python < 3.7. v2.12 was the last release supporting Python 3.6."
     raise ImportError(msg)