add JDK8 notes to the migration guide and README files

Author: lbalmaceda

README.md

@@ -12,7 +12,22 @@ Android Java & Kotlin toolkit for consuming the Auth0 Authentication API
 
 ## Requirements
 
-Android API version 21 or newer
+Android API version 21 or later and Java 8+.
+
+Here’s what you need in `build.gradle` to target Java 8 byte code for Android and Kotlin plugins respectively.
+
+```groovy
+android {
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+}
+```
 
 ## Installation
 

V2_MIGRATION_GUIDE.md

@@ -4,7 +4,22 @@ v2 of the Auth0 Android SDK includes a number of improvements to integrating Aut
 
 ## Requirements changes
 
-v2 requires Android API version 21 or later.
+v2 requires Android API version 21 or later and Java 8+.
+
+Here’s what you need in `build.gradle` to target Java 8 byte code for Android and Kotlin plugins respectively.
+
+```groovy
+android {
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+}
+```
 
 ## OIDC only
 

auth0/src/main/java/com/auth0/android/provider/IdTokenVerifier.java

@@ -11,11 +11,7 @@
 import static android.text.TextUtils.isEmpty;
 
 class IdTokenVerifier {
-    private static final Integer DEFAULT_CLOCK_SKEW = 60; //1 min = 60 sec
-
-    private static final String NONCE_CLAIM = "nonce";
-    private static final String AZP_CLAIM = "azp";
-    private static final String AUTH_TIME_CLAIM = "auth_time";
+    private static final Integer DEFAULT_CLOCK_SKEW = 60; // 1 min = 60 sec
 
     /**
      * Verifies a provided ID Token follows the OIDC specification.