Override config parameters rather than merging them.

Config parameters were merged recursively down to any depth of hashes.
There's actually no reason to do this. Only one level needs merging,
and that is the parameters under each cop name. The only cop that
currently has a parameter that is a hash, is CollectionMethods.
Merge pull request #347 from jonas054/fix_config_merge_340

Override config parameters rather than merging them.