node: Change short for graphman prune --history to -y

Using `-h` here conflicts with the autogenerated help option, and it seems
better to keep `-h` for help even though `-y` for history is a bit goofy

Author: lutter

node/src/bin/manager.rs

@@ -230,7 +230,7 @@ pub enum Command {
         #[clap(long, short, default_value = "0.20")]
         prune_ratio: f64,
         /// How much history to keep in blocks
-        #[clap(long, short, default_value = "10000")]
+        #[clap(long, short = 'y', default_value = "10000")]
         history: usize,
     },