Add typescript testing

[tkow]

• Separate Pull requests of Feature/add withT interface #1164

If it isn't needed, close it.

[coveralls]

Coverage remained the same at 88.413% when pulling a3547e2 on tkow:feature/add_dts_test into a06a2c4 on i18next:master.

[rosskevin]

@jamuhl is travis not running the test script? This PR should be broken at this point, I was just checkpointing some changes to the ts setup and I know they are broken locally. Sinc. show all checks just shows code climate I'm concerned that PRs are not being tested.

[jamuhl]

@rosskevin shows failed on https://travis-ci.org/i18next/i18next but not here...will need to check why

[rosskevin]

oh, shows building now...

[jamuhl]

@rosskevin still worked here: #1163

[jamuhl]

@rosskevin might have been just a glitch