Small typo in README.md

I also tried to clone the app and get it running using the instructions, but I got the following failure:

```
Could not find artifact io.pedestal:pedestal.app:jar:0.1.8-SNAPSHOT in clojars (https://clojars.org/repo/)
Could not find artifact io.pedestal:pedestal.app-tools:jar:0.1.8-SNAPSHOT in clojars (https://clojars.org/repo/)
```