Changed the JUnit version dependency from 3.8.2 to 4.0

The SingleCertValidatingFactoryTest class imports symbols from the
org.junit package, which was introduced in JUnit4.
Changed the test README to reflect the new JUnit4 dependency.

The SingleCertValidatingFactoryTest class imports symbols from the
org.junit package, which was introduced in JUnit4.
Merge pull request #177 from dventimi/master

Changed the test README doc to indicate JUnit4 is now needed