Replaces feuerlabs/exometer with basho/exometer

    Removes the folsom dependency and replaces feuerlabs/exometer with
    basho/exometer to sync bear, meck, and folsom dependencies with
    the rest of the Riak stack.
Merge pull request #668 from basho/jsb/fix-exometer-folsom-deps

Replaces feuerlabs/exometer with basho/exometer

Reviewed-by: engelsanchez