Upgrade Surefire 2.21.0 -> 2.22.0 (#31)

See:
- https://issues.apache.org/jira/projects/SUREFIRE/versions/12343247
- apache/maven-surefire@surefire-2.21.0...surefire-2.22.0

pom.xml

@@ -81,7 +81,7 @@
         <version.maven>3.5.3</version.maven>
         <version.nullaway>0.5.4</version.nullaway>
         <version.plexus-compiler>2.8.4</version.plexus-compiler>
-        <version.surefire>2.21.0</version.surefire>
+        <version.surefire>2.22.0</version.surefire>
         <!-- Our build system (Travis CI) provides a monotonically increasing
         build number. When building locally, this number is obviously absent.
         So we provide a default value. -->