Make the test be runnable

matrix-sdk-android/build.gradle

@@ -33,6 +33,8 @@ android {
         targetSdkVersion 28
         versionCode 1
         versionName "0.0.1"
+        // Multidex is useful for tests
+        multiDexEnabled true
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
 
         buildConfigField "String", "GIT_SDK_REVISION", "\"${gitRevision()}\""
@@ -66,6 +68,11 @@ android {
     lintOptions {
         lintConfig file("lint.xml")
     }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }
 
 static def gitRevision() {