PR python/18380 points out that the example in the "help python" text
will only work in Python 2. This changes the example to be valid
syntax for both Python 2 and Python 3.
gdb/ChangeLog
2018-09-10 Tom Tromey <tom@tromey.com>
PR python/18380:
* python/python.c (_initialize_python): Make example in "python"
help work in Python 3.