chore: release 0.3.1

Trims the body before signing it, so a trailing newline from the compose
buffer no longer ends up in the payload. A published record can't contain a
line break, so every post sent from here to a twtxt feed was refused.

Builds against fumi-core 0.1.1, which hands an accept token to a contact once
instead of attaching it to every message.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "carrier"
-version = "0.3.0"
+version = "0.3.1"
 edition = "2021"
 description = "A minimalist smolmail client built on fumi-core, with a Relm4 UI"
 license = "Apache-2.0"