chore(readme): fix mixed content on the readme file (#38)

Author: EugeneHlushko

README.md

@@ -103,7 +103,7 @@ Please take a moment to read our contributing guidelines if you haven't yet done
 [node-url]: https://nodejs.org
 [deps]: https://david-dm.org/webpack-contrib/json5-loader.svg
 [deps-url]: https://david-dm.org/webpack-contrib/json5-loader
-[tests]: http://img.shields.io/travis/webpack-contrib/json5-loader.svg
+[tests]: https://img.shields.io/travis/webpack-contrib/json5-loader.svg
 [tests-url]: https://travis-ci.org/webpack-contrib/json5-loader
 [cover]: https://codecov.io/gh/webpack-contrib/json5-loader/branch/master/graph/badge.svg
 [cover-url]: https://codecov.io/gh/webpack-contrib/json5-loader