Error running sample: "Attempting to call unbound fn"

[Felipe Bueno]

➜  sample git:(master) lein skummet jar
Exception in thread "main" java.lang.IllegalStateException: Attempting to call unbound fn: #'clojure.core/require
    at clojure.lang.Var$Unbound.throwArity(Var.java:43)
    at clojure.lang.AFn.invoke(AFn.java:32)
    at clojure.lang.Var.invoke(Var.java:407)
    at clojure.main.main(main.java:36)
Compilation failed: Subprocess failed
➜  sample git:(master) lein version
Leiningen 2.5.0 on Java 1.7.0_67 Java HotSpot(TM) 64-Bit Server VM

[Oleksandr Yakushev]

You didn't have -ignore-lean-classes=true option, did you?