Update Maven Surfire and Failsafe plugins from 2.19.1 to 2.20.
<javadoc.plugin.version>2.10.4</javadoc.plugin.version>
<!-- surefire.plugin.version 2.18 yields http://jira.codehaus.org/browse/SUREFIRE-1121, which is fixed in 2.18.1 -->
<!-- surefire.plugin.version 2.19 yields https://issues.apache.org/jira/browse/SUREFIRE-1193. -->
- <surefire.plugin.version>2.19.1</surefire.plugin.version>
- <failsafe.plugin.version>2.19.1</failsafe.plugin.version>
+ <surefire.plugin.version>2.20</surefire.plugin.version>
+ <failsafe.plugin.version>2.20</failsafe.plugin.version>
<checkstyle.plugin.version>2.17</checkstyle.plugin.version>
<rat.plugin.version>0.12</rat.plugin.version>
<pdf.plugin.version>1.2</pdf.plugin.version>
