Fix changelog for 4.0.1 (#93)

PR #72 landed in 4.0.1, not 4.0.0.

Also: add UNRELEASED section

CHANGELOG.md

@@ -1,13 +1,15 @@
+# UNRELEASED
+
 # matrix-sdk-crypto-wasm v4.0.1
 
 -   `PickledInboundGroupSession.sender_signing_key` is now optional.
     ([#89](https://github.com/matrix-org/matrix-rust-sdk-crypto-wasm/pull/89))
 
-# matrix-sdk-crypto-wasm v4.0.0
-
 -   Properly encode missing and `Duration` parameters in requests.
     ([#72](https://github.com/matrix-org/matrix-rust-sdk-crypto-wasm/pull/72))
 
+# matrix-sdk-crypto-wasm v4.0.0
+
 **BREAKING CHANGES**
 
 -   Rename `OlmMachine.init_from_store` introduced in v3.6.0 to