Resolve "Internal Changes representation is not working as expected"

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Closes #152

nucleus/change.go

@@ -141,7 +141,15 @@ func stateManager(ch *Change, timeout time.Duration) (chan<- ppb.Change_State, <
 				if ch.state == ppb.Change_CONFIRMED {
 					continue
 				}
-				err := ch.callback(ch.intendedState, ch.previousState)
+
+				//TODO: debug -> remove
+				ch.lock.Lock()
+				intendedStateCopy := ch.intendedState
+				previousStateStateCopy := ch.previousState
+				ch.lock.Unlock()
+				// END
+
+				err := ch.callback(intendedStateCopy, previousStateStateCopy)
 				if err != nil {
 					ch.lock.Lock()
 					ch.state = ppb.Change_INCONSISTENT