chore(graphcache): Bump version [deprecate v5.1.0]
The version @urql/exchange-graphcache@5.1.0 has accidentally
been published by a flawed canary release script. We're
bumping the version here, but the published `5.1.0` on
the npm registry has been flagged as deprecated with:
> Invalid Release: 5.1.0 has been an accidental and incomplete release