(maint) Use Timer::elapsed_milliseconds
(maint) Use Timer::elapsed_milliseconds

Using the integer milliseconds value instead of casting the WebSocket
connection timout to a double (in seconds); the new member function is
provided by the new Leatherman 0.7.2 release.

MikaelSmith/cpp-pcp-client,puppetlabs/cpp-pcp-client,puppetlabs/cpp-pcp-client,MikaelSmith/cpp-pcp-client,MikaelSmith/cpp-pcp-client,puppetlabs/cpp-pcp-client,MikaelSmith/cpp-pcp-client,puppetlabs/cpp-pcp-client,MikaelSmith/cpp-pcp-client