message: need mut self for Api trait
diff: @@ -4,11 +4,11 @@ use storage::{Storage, types::{PackHash}};
  use network::{Result};
  pub trait Api {
  - fn get_tip(&self) -> Result<BlockHeader>;
  + fn get_tip(&mut self) -> Result<BlockHeader>;
  - fn get_block(&self) -> Result<Block>;
  + fn get_block(&mut self) -> Result<Block>;
  - fn fetch_epoch(&self, storage: &mut Storage, fep: FetchEpochParams) -> Result<FetchEpochResult>;
  + fn fetch_epoch(&mut self, storage: &mut Storage, fep: FetchEpochParams) -> Result<FetchEpochResult>;
  }
  #[derive(Debug)]
  