prettier doesn't seem to work on our .sol files

[geoknee]

If I run yarn prettier:check (which is hooked into our linting check on circle), I get an error printed but still get a successful exit code:

➜  statechannels-contracts git:(solidity-prettier) ✗ yarn prettier:check
yarn run v1.22.5
$ prettier --list-different **/*.sol
contracts/AttestationApp.sol[error] No parser could be inferred for file: contracts/AttestationApp.sol
✨  Done in 0.58s.

No formatting is applied as a result.