[Proposal] Give @kvark reviewer privileges.

kvark has make several important contributions to webrender,
both as a reviewer and committer. He also has significant
Rust experience previously as the author of gfx-rs.

Some examples of recent reviews:

servo/webrender#546
servo/webrender#523
servo/webrender#561
servo/webrender#554

Author: gw3583

homu/files/cfg.toml

@@ -179,6 +179,7 @@ secret = "{{ pillar["homu"]["web-secret"] }}"
     "jgraham",
     "KiChjang",
     "kmcallister",
+    "kvark",
     "larsbergstrom",
     "Manishearth",
     "mbrubeck",