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

Request Type: docs

How to reproduce: 
1. Go to https://docs.angularjs.org/api/ng/service/$interval 
2. View example - bindings not complete and buttons do not work

Component(s): $interval

Impact: small

Complexity: small

This issue is related to: N/A

**Detailed Description:**
The docs example was missing closing `]` for dependency injections.

**Other Comments:**
N/A