Allow MessageFormat v2.x

[tregusti]

Subject of the issue

Allow v2 of MessageFormat.

Your environment

• version of angular-translate: 2.17.0
• version of angular: 1.5

Request

MessageFormat 2.x is out, and I'd like to use it. AFAIK, the breaking changes does not affect the API towards it, only the outcome of the formats. So it should perhaps be a major version bump for the messageformat interpolator, but not for angular-translate itself. I did not understand how the versioning worked for the specific plugin though. If at all distinct/different from angular-translate.

Just installing v2 in this repo and running the tests works like a charm, but I don't know what more is needed to run tests for different angular versions or for being able to create a working mergable PR. Please advise if you want me to do it. Just bumping in bower.js seemed to work...

[knalli]

@tregusti "Allow" would imply we forbid it. That is not true. ;) So yes: Just install the version you want and override this decision with a custom resolution in case of bower. In npm, I think package-lock is your friend...

Speaking of testability in general, we have in test/scopes/ setups for test runnings against multiple AJS framework versions. If nothing breaks, a new default for 2 is okay, but a test against 1 should be exist for legacy support. The actual unit tests are here: https://github.com/angular-translate/angular-translate/blob/b633bf8c4740de9c867e83c48cc60b1a79b06016/test/unit/service/messageformat-interpolation.spec.js Maybe we can extend here some?