Fix typo (id_rsa_pub -> id_rsa.pub) in code sample.

Reported by Peizhao Hu.
7 jobs for master in 1 minute and 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #2446
apt

00:00:38

passed #2447
cloudlab

00:01:36

passed #2448
emulab

00:00:42

passed #2449
phantomnet

00:00:37

passed #2450
powder

00:00:41

 
  Deploy
passed #2451
pages

00:00:21

passed pages:deploy

00:00:01