Use CircleCI as primary CI tool.

Author: ghengeveld

README.md

@@ -14,8 +14,8 @@
   <a href="https://bundlephobia.com/result?p=react-async">
     <img src="https://img.shields.io/bundlephobia/min/react-async.svg" alt="minified size">
   </a>
-  <a href="https://travis-ci.org/ghengeveld/react-async">
-    <img src="https://img.shields.io/travis/ghengeveld/react-async/master.svg" alt="build status">
+  <a href="https://circleci.com/gh/ghengeveld/react-async">
+    <img src="https://img.shields.io/circleci/build/github/ghengeveld/react-async/master.svg" alt="build status">
   </a>
   <a href="https://codecov.io/github/ghengeveld/react-async">
     <img src="https://img.shields.io/codecov/c/github/ghengeveld/react-async/master.svg" alt="code coverage">