Merge pull request #249 from lluchs/clang-absolute-value

Fix warning in clang 3.5 (-Wabsolute-value)

src/vm/wren_core.c

@@ -396,7 +396,7 @@ static uint32_t calculateRange(WrenVM* vm, Value* args, ObjRange* range,
   }
 
   uint32_t to = (uint32_t)value;
-  *length = abs(from - to) + 1;
+  *length = abs((int)(from - to)) + 1;
   *step = from < to ? 1 : -1;
   return from;
 }