Bump mockito-core from 2.23.0 to 2.23.4

Bumps [mockito-core](https://github.com/mockito/mockito) from 2.23.0 to 2.23.4.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v2.23.0...v2.23.4)

Signed-off-by: dependabot[bot] <support@dependabot.com>

build.gradle

@@ -245,7 +245,7 @@ dependencies {
 
     // dependencies for local unit tests
     testImplementation 'junit:junit:4.12'
-    testImplementation 'org.mockito:mockito-core:2.23.0'
+    testImplementation 'org.mockito:mockito-core:2.23.4'
     // dependencies for instrumented tests
     // JUnit4 Rules
     androidTestImplementation 'com.android.support.test:rules:1.0.2'