Fix debug warning in case of trailing comma in function

[garthenweb]

When using trailing comma in a function within the t function the scanner throws an error because an empty string is passed to the esprima parser.

This PR includes a test case as well as the fix. Please let me know if you have a better idea on how to fix it or how to implement the test case.

The script is still working as expected without the fix, because the error is catched, but the it logs an error in debug mode which is first annoying and second reduces trust into the library.

[coveralls]

Coverage increased (+0.2%) to 90.87% when pulling 4770abf on garthenweb:bugfix/trailing-comma into 41165bb on i18next:master.

[TylerK]

@garthenweb Great find, I'm having this exact issue right now with our application. Prettier will format long strings as function params as such:

Before Prettier formatting:

const longString = t('lorem ipsum...');

After Prettier formatting:

const longString = t(
  'lorem ipsum...',
);

[garthenweb]

@TylerK Happy to hear that it's helpful!
@cheton Any objections on this?