Fix typo, hasCode -> hashCode

Author: robinst

Scalatron/doc/markdown/Scalatron Tutorial.md

@@ -1795,7 +1795,7 @@ The modifier keyword `case` before the `class` keyword basically instructs the c
 
 * an immutable field for each parameter of the `class` definition  
 * an `equals()` method that tests equality by checking each field 
-* a `hasCode` method that takes into account each field 
+* a `hashCode` method that takes into account each field 
 * a `toString` method that takes into account each field 
 
 as well as a few others. Upgrading a `class` to a `case class` also automatically