bot_config: Avoid deprecated ConfigParser.readfp method.
bot_config: Avoid deprecated ConfigParser.readfp method.

Fixes this warning with python -Wd:

/home/circleci/zulip/zerver/lib/bot_config.py:69: DeprecationWarning: This method will be removed in future versions.  Use 'parser.read_file()' instead.
  config.readfp(conf)

https://docs.python.org/3/library/configparser.html#configparser.ConfigParser.readfp

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

eeshangarg/zulip,rht/zulip,brainwane/zulip,andersk/zulip,synicalsyntax/zulip,timabbott/zulip,kou/zulip,timabbott/zulip,hackerkid/zulip,showell/zulip,shubhamdhama/zulip,showell/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,timabbott/zulip,timabbott/zulip,zulip/zulip,synicalsyntax/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,synicalsyntax/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,timabbott/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,rht/zulip,brainwane/zulip,brainwane/zulip,hackerkid/zulip,synicalsyntax/zulip,hackerkid/zulip,hackerkid/zulip,eeshangarg/zulip,shubhamdhama/zulip,showell/zulip,zulip/zulip,kou/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,showell/zulip,rht/zulip,zulip/zulip,brainwane/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,synicalsyntax/zulip,brainwane/zulip,zulip/zulip,rht/zulip,shubhamdhama/zulip,andersk/zulip,zulip/zulip,andersk/zulip,shubhamdhama/zulip,showell/zulip,eeshangarg/zulip,punchagan/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,kou/zulip,showell/zulip,andersk/zulip,kou/zulip,shubhamdhama/zulip,punchagan/zulip,shubhamdhama/zulip,rht/zulip,rht/zulip,brainwane/zulip,synicalsyntax/zulip