Update app/src/main/java/com/azuresamples/msalandroidapp/StaticTokenAuthProvider.java

Co-authored-by: Vincent Biret <vincentbiret@hotmail.com>

Author: jasonjoh

app/src/main/java/com/azuresamples/msalandroidapp/StaticTokenAuthProvider.java

@@ -47,7 +47,7 @@
  */
 public class StaticTokenAuthProvider extends BaseAuthenticationProvider {
 
-    private String mAccessToken;
+    private final String mAccessToken;
 
     public StaticTokenAuthProvider(String accessToken) {
         mAccessToken = accessToken;