check_gwdatafind_latency plugin broken by gwdatafind client 2.1.0

GWDataFind client 2.1.0 introduces support for multiple server APIs, which required restructuring the gwdatafind.api module into a subpackage. As a result the check_gwdatafind_latency plugin is now broken. See e.g. here:

Traceback (most recent call last):
  File "/usr/lib/nagios/plugins/check_gwdatafind_latency", line 5, in
    from igwn_monitor.plugins.check_gwdatafind_latency import main
  File "/usr/lib/python3/dist-packages/igwn_monitor/plugins/check_gwdatafind_latency.py", line 12, in
    from gwdatafind.api import find_latest_path
ImportError: cannot import name 'find_latest_path' from 'gwdatafind.api' (/usr/lib/python3/dist-packages/gwdatafind/api/__init__.py)

Should be an easy fix.