Sync to latest grin master and fix missing verifier_cache

[trevyn]

As reported by @tromp in keybase://chat/grincoin.teams.wallet_dev#general/8552 :

it looks like grin-wallet is out of sync with grin ?!
grin master removed verifier cache from calls like Chain::init
but it's still passed in e.g. https://github.com/mimblewimble/grin-wallet/blob/master/impls/src/test_framework/testclient.rs#L105
shldn't there be a grin-wallet complement to your commit mimblewimble/grin@f6ec77a ?

Bumps Cargo.lock mimblewimble/grin git dependencies to latest commit mimblewimble/grin@f6ec77a and fixes the disappearance of the verifier cache.

cargo test --all passes locally.

Unblocks #479.

[antiochp]

👍