Update README for Travis CI Badge

### Updating Badge link to the newTravis CI link.
- Update badge root to `api.travis-ci.com` (new)
  from `travis-ci.org` (old), which was migrated.

README.md

@@ -17,8 +17,8 @@ a list of known ports and bindings is provided on [Zstandard homepage](http://ww
 [![Build status][CirrusDevBadge]][CirrusLink]
 [![Fuzzing Status][OSSFuzzBadge]][OSSFuzzLink]
 
-[travisDevBadge]: https://travis-ci.org/facebook/zstd.svg?branch=dev "Continuous Integration test suite"
-[travisLink]: https://travis-ci.org/facebook/zstd
+[travisDevBadge]: https://api.travis-ci.com/facebook/zstd.svg?branch=dev "Continuous Integration test suite"
+[travisLink]: https://travis-ci.com/facebook/zstd
 [AppveyorDevBadge]: https://ci.appveyor.com/api/projects/status/xt38wbdxjk5mrbem/branch/dev?svg=true "Windows test suite"
 [AppveyorLink]: https://ci.appveyor.com/project/YannCollet/zstd-p0yf0
 [CircleDevBadge]: https://circleci.com/gh/facebook/zstd/tree/dev.svg?style=shield "Short test suite"