Increment protocol version

Author: quh4gko8

src/main/java/app/attestation/server/AttestationProtocol.java

@@ -128,7 +128,7 @@ class AttestationProtocol {
     // the outer signature and the rest of the chain for pinning the expected chain. It enforces
     // downgrade protection for the OS version/patch (bootloader/TEE enforced) and app version (OS
     // enforced) by keeping them updated.
-    static final byte PROTOCOL_VERSION = 5;
+    static final byte PROTOCOL_VERSION = 6;
     private static final byte PROTOCOL_VERSION_MINIMUM = 5;
     // can become longer in the future, but this is the minimum length
     private static final byte CHALLENGE_MESSAGE_LENGTH = 1 + RANDOM_TOKEN_LENGTH * 2;