Use https for pagecache crates.io merit badge
Like the top level crate, the README for pagecache should also have an HTTPS link here.
# pagecache
[![Build Status](https://travis-ci.org/spacejam/sled.svg?branch=master)](https://travis-ci.org/spacejam/sled)
-[![crates.io](http://meritbadge.herokuapp.com/pagecache)](https://crates.io/crates/pagecache)
+[![crates.io](https://meritbadge.herokuapp.com/pagecache)](https://crates.io/crates/pagecache)
[![documentation](https://docs.rs/pagecache/badge.svg)](https://docs.rs/pagecache)
A construction kit for databases. Provides a lock-free log store and pagecache.
