The JavaScriptCompiler API docs sample code is broken as of 4.6

Just a note, that the [sample code for subclassing JavaScriptCompiler in the docs](https://github.com/handlebars-lang/handlebars.js/blob/master/docs/compiler-api.md#javascript-compiler) is broken as of ~4.6 with:

TypeError: name.toLowerCase is not a function

(It works with handlebars 4.5 but fails with 4.6)

You can test this by swapping the handlebars.js version used in the [linked jsfiddle](https://jsfiddle.net/9D88g/162/) with the latest version (4.7.7).

Start with the JavaScriptCompiler sample in docs/compiler-api.md and reproduce the reported TypeError using the linked JSFiddle with Handlebars 4.7.7. Compare the sample's behavior with 4.5, then update the documentation example so it runs against the current version and verify the corrected snippet in the fiddle.

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