Improve header renaming regular expression

[jsumners-nr]

node-newrelic/lib/header-attributes.js

Lines 97 to 101 in d2fba9d

	// Converts headers in the form 'header-name' to be in the form 'headerName'
	// eslint-disable-next-line sonarjs/slow-regex
	return newHeader.replace(/[\W_]+(\w)/g, function capitalize(m, $1) {
	return $1.toUpperCase()
	})

This regular expression is triggering sonar-js's "slow regex" rule. We need to investigate what the regular expression does, and see if we can improve it.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-354853