Fix deprecations from aasm Gem

aasm is throwing these warnings:

```
.aasm_events is deprecated and will be removed in version 4.0.0; please use .aasm.events instead!
.aasm_initial_state is deprecated and will be removed in version 4.0.0; please use .aasm.initial_state instead!
.aasm_states is deprecated and will be removed in version 4.0.0; please use .aasm.states instead!
Event#all_transitions is deprecated and will be removed in version 4.0.0; please use Event#transitions instead!
```

so basically,
```diff
-    current_class.aasm_events
+    current_class.aasm.events
```
```diff
-      current_class.aasm_initial_state
+     current_class.aasm.initial_state
```
```diff
-    current_class.aasm_states
+    current_class.aasm.states
```
```diff
-      event.all_transitions
+      event.transitions
```