doc: correct styling of _GitHub_ in onboarding doc · nodejs/node@3f78220

Original file line number	Diff line number	Diff line change
`@@ -144,7 +144,7 @@ onboarding session.`
`144`	`144`	`(especially if it just has nits left).`
`145`	`145`	`* Approving a change`
`146`	`146`	`* Collaborators indicate that they have reviewed and approve of the changes in`
`147`		`- a pull request using Github’s approval interface`
	`147`	`+ a pull request using GitHub’s approval interface`
`148`	`148`	* Some people like to comment `LGTM` (“Looks Good To Me”)
`149`	`149`	`* You have the authority to approve any other collaborator’s work.`
`150`	`150`	`* You cannot approve your own pull requests.`