Add sw-cache snippet to the bottom of the template with fingerprinted path

## **BEFORE YOU SUBMIT** please read the following:

* [ ] **I'm submitting a bug report**
* [ ] **I'm submitting a feature request**
* [ x] **I'm submitting a support request**

**webpack version:**
2.5

**sw-precache-webpack-plugin version**:
0.9.2

**Please tell us about your environment:**
OSX 10.x

**Current behavior:**

I'm currently using [sw cache plugin to load the sw cache worker](https://github.com/goldhand/sw-precache-webpack-plugin). I'm following the instructions there (copy the snippet to the bottom of the page:

```html

if ('serviceWorker' in navigator) {
navigator.serviceWorker
.register("/sw-cache.js")
.then(function() {
console.log('Service worker registered!');
})
.catch(function(error) {
console.log('Error registering service worker: ', error);
});
}

```

**Expected/desired behavior:**

Current behaviour is fine, but doesn't take advantage of contenthash resource names from webpack. Now, creating the fingerprint sw cache is easy, injecting it in the template is not. Is there a way to use webpack to inject the snippet with the proper production `"sw-cache.js"` path?

My main issue with this is that, whenever I release a new version of a pwa app with new assets, loading the cached sw-cache is loading the invalidated set of assets.