Upgrade messageformat

[HollyPony]

Update messageformat dependency and update tests according to doc : https://github.com/messageformat/messageformat.js

This is solving installing i18n with npm 5.4 since it's cause by this dependency.

Also, this is a break change update of messageformat so, I don't understand why should work with plurals was "other" instead of "zero" for effective "0" input.

In an other way, "zero", "two", "few" and "many" doesn't work any more so, this is probably a break changing.

After that, it's a npm error and not here.

Closes #325

[coveralls]

Coverage remained the same at 97.908% when pulling 7ee277f on HollyPony:upgrade-messageformat into 11d89da on mashpie:master.

[cartuchogl]

+1
node 8.7.0 bundled npm 5.4.2

[HollyPony]

I'm not sure about how to upgrade the version of i18n-node. I think it's a potential breaking change PR, so a major version respecting the semver.

[cartuchogl]

npm 5.5.1 fix the problem. Node 8 starts LTS at the end of that month. I don't know if a posible release of 8.8.0 comes bundled with a fixed version of npm.

[HollyPony]

Yup, feel free to close this PR. But I think a little package update is not so bad ^^