fix docs for cent repo setup

Signed-off-by: Nathan Williams <nath.e.will@gmail.com>
Upstream-commit: c6e1d982666bbf37da746975c5ba7511ea9c98a1
Component: engine

components/engine/docs/installation/centos.md

@@ -53,7 +53,7 @@ package manager.
 
 3. Add the yum repo.
 
-        $ cat >/etc/yum.repos.d/docker.repo <<-EOF
+        $ echo | sudo tee /etc/yum.repos.d/docker.repo <<-EOF
         [dockerrepo]
         name=Docker Repository
         baseurl=https://yum.dockerproject.org/repo/main/centos/7