Allow hyphen seperated template variables

[YoannMourot]

Allowing template variables like ^foo-bar=barbar:string. This was causing an error Cannot initialize connector "rest": Cannot read property 'type' of undefined' at boot. https://regex101.com/r/HoCufm/1

Checklist

• [ ] DCO (Developer Certificate of Origin) signed in all commits
• [x] npm test passes on your machine
• [ ] New tests added or existing tests modified to cover all changes
• [ ] Code conforms with the style guide
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[dhmlau]

@raymondfeng, do we intend to support - in the template variables?