Change Travis badge to Semaphore badge

[DenBond7]

https://semaphoreci.com/docs/how-to-get-build-badge.html

[tomholub]

:)

[tomholub]

Actually these docs are for semaphore v1. We are using v2 and it's different. I asked support how to add badge.

[tomholub]

They don't support them yet in v2