`update-wasm-grammars.sh` is broken since #716

[Xophmeister]

Btw, the update-wasm-grammars.sh script doesn't seem to work anymore, since nickel (and many other grammars) are no longer in the Cargo.lock. Maybe it should get the revisions from topiary-config/languages.ncl instead?

Originally posted by @jneem in #736 (comment)