docs: fix header parsing that was breaking misc config manpage

[isaacs]

Tiny fix to the header parsing that was breaking npm help 7 config.

[mikemimik]

@isaacs I think if you rebase latest into this branch, you'll get passing tests

[npm-deploy-user]

	angular-quickstart			app-large			app-medium			ember-quickstart			react-app
	prev	current	status	prev	current	status	prev	current	status	prev	current	status	prev	current	status
initial install	41s	36.3s	✅	39.5s	39.6s	✅🐌	34.5s	32.2s	✅	28.1s	26.3s	✅	33.5s	31.9s	✅
repeat install	9.6s	8.8s	✅	8.6s	8s	✅	8.3s	8.1s	✅	7.7s	7.2s	✅	9.1s	8.6s	✅
with warm cache	32.3s	30.2s	✅	33.8s	32.9s	✅	31.3s	30.3s	✅	23.4s	22.5s	✅	29.1s	27.4s	✅
with node_modules	9.2s	8.7s	✅	8.6s	7.5s	✅	9s	7.9s	✅	7.8s	7.2s	✅	9.4s	8.7s	✅
with lockfile	32.6s	28.2s	✅	31s	30.9s	✅	29s	27.1s	✅	21.7s	20s	✅	27.4s	25s	✅
with warm cache and node_modules	9.3s	8.7s	✅	7.9s	7.9s	✅🐌	8.4s	7.9s	✅	7.6s	6.9s	✅	9.2s	8.4s	✅
with warm cache and lockfile	24.7s	23.6s	✅	26.3s	26.9s	✅🐌	24.3s	23.4s	✅	17.8s	15.7s	✅	21.3s	22.5s	✅🐌
with node_modules and lockfile	10.1s	10.2s	✅🐌	9.8s	8.4s	✅	8.6s	8.2s	✅	7.8s	7.3s	✅	9.7s	9s	✅