Update matchers.rb for deprecated chefspec method

In running spec tests against cookbooks that depends on sysctl cookbook, this deprecation warning is raised:

    DEPRECATION] `ChefSpec::Runner.define_runner_method' is deprecated. It is being used in the sysctl_param resource matcher.Please use `ChefSpec.define_matcher' instead. (called from spec/redis_storage_spec.rb:4:in `block (2 levels) in <top (required)>')

See https://github.com/sethvargo/chefspec/commit/5c098627432f2d9737b8c78d6ceb9e2a30011417 for the actual code change.
Merge pull request #14 from miketheman/patch-1

Update matchers.rb for deprecated chefspec method