Bump mockito-core to 2.23.0 to support stable coroutines

Author: jossiwolf

mockito-kotlin/build.gradle

@@ -29,7 +29,7 @@ dependencies {
     compileOnly "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     compileOnly 'org.jetbrains.kotlinx:kotlinx-coroutines-core:0.30.0-eap13'
 
-    compile "org.mockito:mockito-core:2.21.0"
+    compile "org.mockito:mockito-core:2.23.0"
 
     testCompile 'junit:junit:4.12'
     testCompile 'com.nhaarman:expect.kt:1.0.0'