rust-ryu-0.2.6-1.fc30 has broadened its license from just "ASL 2.0" to
"ASL 2.0 or Boost". The upstream change [1] follows the change in the C
original [2].
[1]
https://github.com/dtolnay/ryu/commit/a8d82216155b547c95d05b7689a6f70d535...
[2]
https://github.com/ulfjack/ryu/commit/bc790e9d9389b0f6682f42d366f7c7b7cad...