pom.xml(maven-{surefire,failsafe}-plugin): updated to 2.18.1

@see http://mail-archives.apache.org/mod_mbox/maven-users/201411.mbox/%3CCAK2FUK2o_9oAUcWkAC=pbA5vejMKW0i0Pn9XBBo9cTg2uRFRYg@mail.gmail.com%3E
@see http://mail-archives.apache.org/mod_mbox/maven-users/201412.mbox/%3CCAKuVzBSJPg2zJPpan4g_fQRRH8E_q8ZLH=+1zHABsWsDBEVxGw@mail.gmail.com%3E

No functional changes.