Added fix for javax.script.ScriptException

From top of stack trace:
/Users/java/Documents/git/lwjgl3/build.xml:15: javax.script.ScriptException: ReferenceError: "println" is not defined in <eval> at line number 5

See: https://bugs.openjdk.java.net/browse/JDK-8035181
Replaced tab characters with two spaces.