message: add explicity type in prover.rs
diff: @@ -395,7 +395,7 @@ where
  let alpha_chal = ScalarChallenge(fq_sponge.challenge());
  //~ 18. Derive $\alpha$ from $\alpha'$ using the endomorphism (TODO: details)
  - let alpha = alpha_chal.to_field(&index.srs.endo_r);
  + let alpha: ScalarField<G> = alpha_chal.to_field(&index.srs.endo_r);
  //~ 19. TODO: instantiate alpha?
  let mut all_alphas = index.powers_of_alpha.clone();
  