litrpc: let revoked_at use type 16

Update the proto message field number for revoked_at to be 16 and
reserve 14 and 15 for future use.

Author: ellemouton

litrpc/lit-sessions.pb.go

@@ -93,6 +93,16 @@ message Session {
 
     string account_id = 13;
 
+    /*
+    Field number 14 is reserved for future use.
+    */
+    reserved 14;
+
+    /*
+    Field number 15 is reserved for future use.
+    */
+    reserved 15;
+
     /*
     The unix timestamp indicating the time at which the session was revoked.
     Note that this field has not been around since the beginning and so it
@@ -101,7 +111,7 @@ message Session {
     readers should not assume that if this field is zero that the session is
     not revoked. Readers should instead first check the session_state field.
     */
-    uint64 revoked_at = 14 [jstype = JS_STRING];
+    uint64 revoked_at = 16 [jstype = JS_STRING];
 }
 
 message MacaroonRecipe {