[Java] Upgrade to Mockito 3.0.0.

Author: mjpt777

build.gradle

@@ -140,13 +140,11 @@ subprojects {
         compile 'org.agrona:agrona:1.0.3'
 
         testCompile 'org.hamcrest:hamcrest:2.1'
-        testCompile 'org.mockito:mockito-core:2.28.2'
+        testCompile 'org.mockito:mockito-core:3.0.0'
         testCompile 'junit:junit:4.12'
     }
 
-    checkstyle {
-        toolVersion = '8.22'
-    }
+    checkstyle.toolVersion = '8.22'
 
     compileJava {
         sourceCompatibility = sbeJavaVersion