Remove Mastodon link from README

Closes #662.

README.md

@@ -59,7 +59,6 @@ issued at the discretion of the Immunefi program managers.
 - [Website](https://serai.exchange/): https://serai.exchange/
 - [Immunefi](https://immunefi.com/bounty/serai/): https://immunefi.com/bounty/serai/
 - [Twitter](https://twitter.com/SeraiDEX): https://twitter.com/SeraiDEX
-- [Mastodon](https://cryptodon.lol/@serai): https://cryptodon.lol/@serai
 - [Discord](https://discord.gg/mpEUtJR3vz): https://discord.gg/mpEUtJR3vz
 - [Matrix](https://matrix.to/#/#serai:matrix.org): https://matrix.to/#/#serai:matrix.org
 - [Reddit](https://www.reddit.com/r/SeraiDEX/): https://www.reddit.com/r/SeraiDEX/

substrate/coins/pallet/Cargo.toml

@@ -35,7 +35,7 @@ serai-primitives = { path = "../../primitives", default-features = false, featur
 coins-primitives = { package = "serai-coins-primitives", path = "../primitives", default-features = false }
 
 [dev-dependencies]
-sp-io = { git = "https://github.com/serai-dex/substrate", default-features = false }
+sp-io = { git = "https://github.com/serai-dex/substrate", default-features = false, features = ["std"] }
 
 [features]
 std = [
@@ -44,7 +44,6 @@ std = [
 
   "sp-core/std",
   "sp-std/std",
-  "sp-io/std",
   "sp-runtime/std",
 
   "pallet-transaction-payment/std",