update okhttp3:mockwebserver to 4.2.1 (#1)

Author: wnchen

tester/build.gradle

@@ -6,10 +6,9 @@ dependencies {
     api 'com.google.code.gson:gson:2.8.5'
     api 'org.mockito:mockito-core:2.23.4'
     api 'pl.pragmatists:JUnitParams:1.1.1'
-    api 'com.squareup.okhttp3:mockwebserver:3.12.1'
     api "org.assertj:assertj-core:3.11.1"
     api "org.robolectric:robolectric:3.8"
-    api "com.squareup.okhttp3:mockwebserver:3.12.1"
+    api "com.squareup.okhttp3:mockwebserver:4.2.1"
     api "com.google.firebase:firebase-admin:6.4.0"
     api "com.google.guava:guava:27.0.1-jre"