doc: update contrib docs

_contrib/contributing.md

@@ -8,7 +8,7 @@ You want to contribute? You're awesome! Don't know where to start? Check the [li
 [easy tag]: https://github.com/hyperium/hyper/issues?q=label%3AE-easy+is%3Aopen
 
 
-## [Pull Requests](pull_requests.md)
+## [Pull Requests](pull-requests.md)
 
-- [Submitting a Pull Request](pull_requests.md#submitting-a-pull-request)
+- [Submitting a Pull Request](pull-requests.md#submitting-a-pull-request)
 - [Commit Guidelines](commits.md)

_contrib/governance.md

@@ -109,6 +109,6 @@ Maintainers are the project admins. Besides being a collaborator, they take care
 of house-keeping duties, help lead the direction, and have the final authority when
 required.
 
-[coc]: ./code_of_conduct.md
+[coc]: ./code-of-conduct.md
 [contrib]: ../contributing.md
 [triage-guide]: ./issues.md#triaging

_contrib/issues.md

@@ -112,6 +112,6 @@ The severity marks how _severe_ the issue is. Note this isn't "importance" or "p
 - **S-refactor**: improve internal code to help readability and maintenance.
 
 [issues]: https://github.com/hyperium/hyper/issues
-[COC]: ./code_of_conduct.md
-[PRs]: ./pull_requests.md
+[COC]: ./code-of-conduct.md
+[PRs]: ./pull-requests.md
 [MRE]: https://en.wikipedia.org/wiki/Minimal_reproducible_example

_contrib/tenets.md

@@ -20,7 +20,7 @@ community building and using it. All contributions are in the open. We don't
 maintain private versions, and don't include features that aren't useful to
 others.
 
-[We prioritize kindness](./code_of_conduct.md), compassion and empathy towards all
+[We prioritize kindness](./code-of-conduct.md), compassion and empathy towards all
 contributors. Technical skill is not a substitute for human decency.
 
 ### Examples