Check argument is associate list

I got following error when argument of 'helm-chrome--add-bookmark' is
'(meta_info . "{\"sync\":{\"transaction_version\":\"113\"}}")'.

    cond: Wrong type argument: listp, "{\"sync\":{\"transaction_version\":\"113\"}}"
    Beginning of buffer
Merge pull request #3 from syohex/improve-json-parsing

Check argument is associate list