Update to Mockito 2.18.3.

This also swaps out the dependency on mockito-all with mockito-core, which is actually maintained. The purpose of updating is to allow for new Mockito features, such as mocking final methods, which happens due to the test resource org.mockito.plugins.MockMaker.

pom.xml

@@ -97,8 +97,8 @@
     <!-- Mockito -->
     <dependency>
       <groupId>org.mockito</groupId>
-      <artifactId>mockito-all</artifactId>
-      <version>1.10.19</version>
+      <artifactId>mockito-core</artifactId>
+      <version>2.18.3</version>
     </dependency>
   </dependencies>
 </project>

src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker

@@ -0,0 +1 @@
+mock-maker-inline