use default interpolator instead of return original translationId

[tsaikd]

if not define translationId

before:
$filter("translate")("Name: {{name}}", {name: "User"}) // "Name: {{name}}"

after:
$filter("translate")("Name: {{name}}", {name: "User"}) // "Name: User"

[knalli]

Yes, I this looks like a feature :)

1. Please follow contribution guide lines: create a branch based on the latest canary, apply your changes and make a PR against canary
2. please add a test ensure this will work

[knalli]

replaced by #730