Bug: @newInstance() becomes container default instance if it's the first instance

Nobody has claimed this yet.

**I'm submitting a bug report**

* **Library Version:**
1.5.2

This is a regression from v1.4.2, where this worked correctly. I tried to implement the same test for that version, but had issues getting everything to build and run for that tag. The new TS repo structure and scripts are much appreciated. :)

**Please tell us about your environment:**
* **Operating System:**
Linux (Ubuntu 18.04)

* **Node Version:**
10.16

* **NPM Version:**
N/A

* **JSPM OR Webpack AND Version**
N/A

* **Browser:**
all

* **Language:**
all

**Current behavior:**
https://github.com/krisdages/aurelia-dependency-injection/tree/bugtest/new-instance-injects-default
```typescript
// test/resolver.spec.ts
// PASSES, as expected
it('get a new instance of a dependency, without regard for existing instances in the container', () => {
const container = new Container();
const logger = container.get(Logger);
const newLogger = container.get(NewInstance.of(Logger));

expect(logger).toEqual(jasmine.any(Logger));
expect(newLogger).toEqual(jasmine.any(Logger));
expect(newLogger).not.toBe(logger);
});

//FAILS
it('new instance of a dependency does not become the default instance in the container', () => {
const container = new Container();
//only difference is the order of the gets.
const newLogger = container.get(NewInstance.of(Logger));
const logger = container.get(Logger);

expect(logger).toEqual(jasmine.any(Logger));
expect(newLogger).toEqual(jasmine.any(Logger));
expect(newLogger).not.toBe(logger);
});
```

**Expected/desired behavior:**
Both tests should pass.

clone or checkout https://github.com/krisdages/aurelia-dependency-injection
```shell
git clone https://github.com/krisdages/aurelia-dependency-injection
git checkout bugtest/new-instance-injects-default
npm install
npm run test
```

* **What is the expected behavior?**

* **What is the motivation / use case for changing the behavior?**
This is a regression from version 1.4

Start with test/resolver.spec.ts and reproduce the two get-order cases from the issue. Run npm install followed by npm run test, then compare the behavior with the expected results: retrieving NewInstance.of(Logger) first must not make that object the container's default Logger instance, and both tests should pass.

Written by the indexing model from the issue text.