[hab-sup] Handlebars templates don't allow -

[bookshelfdave]

Since bumping the Handlebars Rust dep to 0.19.0,
we're no longer able to render templates that contain - in a Handlebars expression. For example:

backlog {{tcp-backlog}}

will fail with

hab-sup(ER)[src/error.rs:325:8]: TemplateError(InvalidSyntax(54, 22))

I've submitted a PR to potentially resolve the issue, as it also appears on handlebars-rust master:
sunng87/handlebars-rust#94

[bookshelfdave]

This can be closed once #1119 is merged.

😸