[skip ci] Use HTTPS in README

This should fix mixed-content issue in YARD documentations.

Author: FranklinYu

README.md

@@ -5,7 +5,7 @@
 [![Dependency Status](https://gemnasium.com/ruby-grape/grape.svg)](https://gemnasium.com/ruby-grape/grape)
 [![Code Climate](https://codeclimate.com/github/ruby-grape/grape.svg)](https://codeclimate.com/github/ruby-grape/grape)
 [![Coverage Status](https://coveralls.io/repos/github/ruby-grape/grape/badge.svg?branch=master)](https://coveralls.io/github/ruby-grape/grape?branch=master)
-[![Inline docs](http://inch-ci.org/github/ruby-grape/grape.svg)](http://inch-ci.org/github/ruby-grape/grape)
+[![Inline docs](https://inch-ci.org/github/ruby-grape/grape.svg)](https://inch-ci.org/github/ruby-grape/grape)
 [![git.legal](https://git.legal/projects/1364/badge.svg "Number of libraries approved")](https://git.legal/projects/1364)
 [![Join the chat at https://gitter.im/ruby-grape/grape](https://badges.gitter.im/ruby-grape/grape.svg)](https://gitter.im/ruby-grape/grape?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)