Update to latest Travis CI Build Status

https://travis-ci.com/gabime/spdlog (404's) → https://app.travis-ci.com/github/gabime/spdlog
https://travis-ci.com/gabime/spdlog.svg?branch=v1.x → https://app.travis-ci.com/gabime/spdlog.svg?branch=v1.x (Result from clicking Status Image url builder)

README.md

@@ -1,6 +1,6 @@
 # spdlog
 
-Very fast, header-only/compiled, C++ logging library. [![Build Status](https://travis-ci.com/gabime/spdlog.svg?branch=v1.x)](https://travis-ci.com/gabime/spdlog)  [![Build status](https://ci.appveyor.com/api/projects/status/d2jnxclg20vd0o50?svg=true)](https://ci.appveyor.com/project/gabime/spdlog) [![Release](https://img.shields.io/github/release/gabime/spdlog.svg)](https://github.com/gabime/spdlog/releases/latest)
+Very fast, header-only/compiled, C++ logging library. [![Build Status](https://app.travis-ci.com/gabime/spdlog.svg?branch=v1.x)](https://app.travis-ci.com/github/gabime/spdlog)  [![Build status](https://ci.appveyor.com/api/projects/status/d2jnxclg20vd0o50?svg=true)](https://ci.appveyor.com/project/gabime/spdlog) [![Release](https://img.shields.io/github/release/gabime/spdlog.svg)](https://github.com/gabime/spdlog/releases/latest)
 
 ## Install 
 #### Header only version