docs(README.md): use https for all links

README.md

@@ -1,7 +1,7 @@
 clap
 ====
 
-[![Crates.io](https://img.shields.io/crates/v/clap.svg)](https://crates.io/crates/clap) [![Crates.io](https://img.shields.io/crates/d/clap.svg)](https://crates.io/crates/clap) [![license](http://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/kbknapp/clap-rs/blob/master/LICENSE-MIT) [![Coverage Status](https://coveralls.io/repos/kbknapp/clap-rs/badge.svg?branch=master&service=github)](https://coveralls.io/github/kbknapp/clap-rs?branch=master) [![Join the chat at https://gitter.im/kbknapp/clap-rs](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/kbknapp/clap-rs?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Crates.io](https://img.shields.io/crates/v/clap.svg)](https://crates.io/crates/clap) [![Crates.io](https://img.shields.io/crates/d/clap.svg)](https://crates.io/crates/clap) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/kbknapp/clap-rs/blob/master/LICENSE-MIT) [![Coverage Status](https://coveralls.io/repos/kbknapp/clap-rs/badge.svg?branch=master&service=github)](https://coveralls.io/github/kbknapp/clap-rs?branch=master) [![Join the chat at https://gitter.im/kbknapp/clap-rs](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/kbknapp/clap-rs?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 Linux: [![Build Status](https://travis-ci.org/kbknapp/clap-rs.svg?branch=master)](https://travis-ci.org/kbknapp/clap-rs)
 Windows: [![Build status](https://ci.appveyor.com/api/projects/status/ejg8c33dn31nhv36/branch/master?svg=true)](https://ci.appveyor.com/project/kbknapp/clap-rs/branch/master)