docs($interval): fix missing square brackets in example

Request Type: docs

How to reproduce: Go to https://docs.angularjs.org/api/ng/service/$interval

View example - bindings not complete and buttons do not work

Component(s): 

Impact: small

Complexity: small

This issue is related to: 

**Detailed Description:**

The docs example was missing closing ] for dependency injections.

**Other Comments:**