Convert old soljs files to Truffle 3.0 (.json).
This package will provide you with the sjsu command to upgrade existing sol.js files to their new JSON format.
npm install -g truffle-soljs-updater
Next, navigate to your directory where .sol.js file exist, then run the updater:
$ cd ./build/contracts
$ sjsu
By default, sjsu will create new .json files but leave the existing .sol.js files alone. To have sjsu clean up for you, use the -f option.
$ sjsu -f