a184066660 Move import inside feature gate (Tobin C. Harding)
Pull request description:
The `String` type is only used if the `serde` feature is enabled, move the import statement inside the already feature gated block.
ACKs for top commit:
apoelstra:
ACK a184066660 successfully ran local tests; sure
Kixunil:
ACK a184066660
Tree-SHA512: 688adb1e4489b0242856ac36ed9cf3503b147b84954cf1e6fd34b5e708ed6c1dd92da91e739243face1c1b4e4c8b19ce88e215117bef2a7af2e732859a6e108a