Fix typo in help.

[anastasiamac]

Description of change

Fixes typo in command help.

QA steps

n/a

Documentation changes

n/a

Bug reference

https://bugs.launchpad.net/juju/+bug/1657642

[anastasiamac]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10768

[anastasiamac]

$$merge$$
bot, how could you fail this landing?...
Unrelated failure:

---

FAIL: oplog_test.go:97: oplogSuite.TestStops

[LOG] 0:00.000 DEBUG juju.testing starting mongo in /mnt/tmp/test-mgo439330007
[LOG] 0:00.000 DEBUG juju.testing found mongod at: "/usr/lib/juju/mongo3.2/bin/mongod"
[LOG] 0:00.081 DEBUG juju.testing started mongod pid 78724 in /mnt/tmp/test-mgo439330007 on port 41625
oplog_test.go:105:
s.getNextOplog(c, tailer)
oplog_test.go:283:
c.Fatal("timed out waiting for oplog doc")
... Error: timed out waiting for oplog doc

[LOG] 0:10.092 DEBUG juju.testing killing mongod pid 78724 in /mnt/tmp/test-mgo439330007 on port 41625 with killed
OOPS: 54 passed, 1 FAILED
--- FAIL: Test (14.17s)

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju