Repl namespace issue

Something is wrong in the namespace setup (I think).
```
--> lein repl
nREPL server started on port 49447 on host 127.0.0.1 - nrepl://127.0.0.1:49447
REPL-y 0.4.3, nREPL 0.6.0
Clojure 1.10.0
Java HotSpot(TM) 64-Bit Server VM 1.8.0_121-b13
Docs: (doc function-name-here)
(find-doc "part-of-name-here")
Source: (source function-name-here)
Javadoc: (javadoc java-object-or-class-here)
Exit: Control+D or (exit) or (quit)
Results: Stored in vars *1, *2, *3, an exception in *e

koan-engine.runner=> (string/join '(1 2 3))
Syntax error compiling at (form-init1178655580028819709.clj:1:1).
No such namespace: string
```
The koans themselves run successfully. This is MacOS. Sorry if I'm doing something dumb.