Update twenty-first/src/util_types/merkle_tree.rs

Co-authored-by: Jan Ferdinand Sauer <ferdinand@neptune.cash>

Author: aszepieniec

twenty-first/src/util_types/merkle_tree.rs

@@ -626,7 +626,7 @@ pub enum MerkleTreeError {
     #[error("The number of leafs must be a power of two.")]
     IncorrectNumberOfLeafs,
 
-    #[error("Tree height must not exceed 63.")]
+    #[error("Tree height implies a tree that does not fit in RAM")]
     TreeTooHigh,
 }