slip-0044: add (satoshilabs#1376)

Author: eckelj

slip-0044.md

@@ -1166,6 +1166,7 @@ Coin type | Path component (`coin_type'`) | Symbol | Coin
 8339  | 0x80002093 | BTQ    | [BitcoinQuark](https://www.bitcoinquark.org)
 8444  | 0x800020fc | XCH    | [Chia](https://www.chia.net)
 8520  | 0x80002148 | ---    | reserved
+8680  | 0x800021e8 | PLMNT  | [Planetmint](https://planetmint.io)
 8888  | 0x800022b8 | SBTC   | [Super Bitcoin](https://www.superbtc.org)
 8964  | 0x80002304 | NULS   | [NULS](https://nuls.io)
 8999  | 0x80002327 | BTP    | [Bitcoin Pay](http://www.btceasypay.com)