Bump mockito-core to 3.12.4 (#444)

Author: vetler

mockito-kotlin/build.gradle

@@ -25,7 +25,7 @@ dependencies {
     compileOnly "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     compileOnly 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.0.0'
 
-    compile "org.mockito:mockito-core:3.9.0"
+    compile "org.mockito:mockito-core:3.12.4"
 
     testCompile 'junit:junit:4.12'
     testCompile 'com.nhaarman:expect.kt:1.0.0'