Babel loose config option causes issues with spread transform

**I'm submitting a bug report**
**I'm submitting a feature request**

* **Library Version:**
1.0.0-beta7

**Please tell us about your environment:**
* **Operating System:**
all

* **Node Version:**
6.2.0

* **NPM Version:**
8.11.3

* **Browser:**
all

* **Language:**
ESNext

* **Loader/bundler:**
all

**Current behavior:**
Babel config specifies `loose: true`. This causes issues when using the spread (`...`) operator with a `Set` object. Specifically, the code:

```javascript
this.foo = [...new Set([1, 2, 3])];
```

is transpiled to

```javascript
this.foo = new Set([1, 2, 3]).concat();
```

This is a problem, as `Set` objects do not have a `concat` method. This transpilation is a consequence of having `loose: true` in `.babelrc.js`, per this issue: https://github.com/babel/babel/issues/7958 . As mentioned in the linked issue, this is the expected behavior when using `loose: true`, and is not a bug in Babel or the spread transformer.

Simply setting `loose: false` will fix this issue.

This issue was originally reported on StackOverflow here: https://stackoverflow.com/questions/53696962/aurelia-not-transpiling-set-and-spread-operator-correctly
* **What is the expected behavior?**
Spread operator to be transpiled correctly with `Set` objects.

* **What is the motivation / use case for changing the behavior?**
Make transpilation work correctly.

Inspect .babelrc.js and the Babel spread-transform configuration first. Reproduce the reported Set spread example with loose mode enabled, then verify the configuration change against the expected transpiled output. Done means the CLI no longer produces a concat call for Set spread, or the issue is documented as configuration behavior.

Written by the indexing model from the issue text.