Fixes Testing against different Clojure Versions

The current form of the alias "all" has the profile `:dev` overwrite the Clojure version of the profiles `:1.2`, `:1.3`, and so on. This means that the only version really tested is `:dev`'s, being "1.5.1".

This can be demonstrated by adding the line

```clojure
(println "--- uses clojure:" *clojure-version*)
```

to e.g. "src/potemkin.clj" and running "lein all do clean, test".

This pull request fixes the issue, making the test results more meaningful.