message: Rename "sapling" to "sapling-crypto" in COPYRIGHT.
diff: -Copyrights in the "sapling" library are retained by their contributors. No
  -copyright assignment is required to contribute to the "sapling" library.
  +Copyrights in the "sapling-crypto" library are retained by their contributors. No
  +copyright assignment is required to contribute to the "sapling-crypto" library.
  -The "sapling" library is licensed under either of
  +The "sapling-crypto" library is licensed under either of
  * Apache License, Version 2.0, (see ./LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
  * MIT license (see ./LICENSE-MIT or http://opensource.org/licenses/MIT)
  