Bump mockito-core from 2.27.0 to 2.28.1 (#1372)

Bumps [mockito-core](https://github.com/mockito/mockito) from 2.27.0 to 2.28.1.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](https://github.com/mockito/mockito/compare/v2.27.0...v2.28.1)

mobile/build.gradle

@@ -136,7 +136,7 @@ dependencies {
     annotationProcessor 'com.google.auto.value:auto-value:1.6.5'
     annotationProcessor 'com.ryanharter.auto.value:auto-value-parcel:0.2.6'
 
-    testImplementation 'org.mockito:mockito-core:2.27.0'
+    testImplementation 'org.mockito:mockito-core:2.28.1'
     testImplementation 'junit:junit:4.12'
     testImplementation 'org.json:json:20180813'
     testImplementation 'com.squareup.okhttp3:mockwebserver:3.12.1'