note we're bumping the dependency version

Since this changed the types of some things it's a PVP "breaking change" and
gets a major version bump.

CHANGELOG.md

 # Changelog for tahoe-ssk
 
+## 0.3.0.0 (Unreleased)
+
+* Updated the tahoe-chk dependency to 0.2.0.0.
+
 ## 0.2.1.0
 
 * Add Ord instances for StorageIndex, Verifier, Reader, and Writer.