Inherit sumo::params instead of including the class

[root@foo ~]# puppet agent --test
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Loading facts
Error: Could not retrieve catalog from remote server: Error 400 on SERVER: "" is not an absolute path. at /etc/puppet/environments/production/modules/sumo/manifests/init.pp:48 on node foo
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run
[root@foo ~]#

Before this change puppet fails to get the value for the sumo::params::config_dir. Running Puppet open source 3.7.3 on CentOS 7.
The escaped double quotes here shouldn't be necessary, if you can change these to single quotes I'll merge your PR.