Issue #681 Fixed RtRepoCommitsITCase.fetchesCommits()

I noticed that all of the commits being checked by the test were pushed on 26 January. The very large number of commits that have been pushed since then has caused the test to perform many, many lookups since this attribute is paginated. One of the commits simply weren't included by the API in the results, because of the sheer size of the result. So what I did was restrict the lookup to a specific time period, which has the side benefit of making the test execute *much* faster.