Bump GSON dependency to 2.8.9

This change bumps [the GSON dependency to 2.8.9](https://github.com/google/gson/releases/tag/gson-parent-2.8.9) to resolve a potential vulnerability in earlier versions of the library reported: https://app.snyk.io/vuln/SNYK-JAVA-COMGOOGLECODEGSON-1730327

Author: evansims

lib/build.gradle

@@ -69,7 +69,7 @@ dependencies {
     implementation 'androidx.recyclerview:recyclerview:1.2.1'
     implementation 'androidx.legacy:legacy-support-v4:1.0.0'
     implementation 'com.google.android.material:material:1.4.0'
-    implementation 'com.google.code.gson:gson:2.8.7'
+    implementation 'com.google.code.gson:gson:2.8.9'
     implementation 'com.squareup:otto:1.3.8'
     api 'com.auth0.android:auth0:2.5.0'
     testImplementation 'junit:junit:4.13.2'
@@ -81,4 +81,4 @@ dependencies {
     testImplementation 'com.squareup.okhttp3:okhttp-tls:4.9.0'
     testImplementation 'com.jayway.awaitility:awaitility:1.7.0'
     testImplementation 'androidx.test.espresso:espresso-intents:3.4.0'
-}
+}