Fix bower.json since empower module does not provide power-assert-formatter any more.
Fix bower.json since empower module does not provide power-assert-formatter any more.

twada/empower-core,twada/power-assert-runtime,jamestalmage/empower-assert,jamestalmage/empower-assert,power-assert-js/empower,power-assert-js/empower,twada/empower-core