Class constructor cannot be invoked without 'new' when extending a class

Hi, I am getting the error "Class constructor cannot be invoked without 'new' " when trying to create a new instance of a class that extends another one.
```
class Parent {}
class Child extends Parent {
constructor(){
super()
}
}
new Child()
```
The error will occur on the line `constructor(){` .
Any ideas on what is causing the error? I think it's due to Babel compiling to the wrong version.

The report names no source file, test, or entry point; start by reproducing the class-extension example in Backpack's build environment and inspect its Babel and webpack configuration. Done means identifying whether transpilation causes the error and recording a verified fix or configuration change, with a regression test if an existing test area is found.

Written by the indexing model from the issue text.