Update build-ref.html
Add a missing indefinite article
Closes
@@ -47,7 +47,7 @@ title: Concepts and Terminology
<h3 id="packages">Packages</h3>
<p>
The primary unit of code organization in a workspace is
- the <i>package</i>. A package is collection of related files and a
+ the <i>package</i>. A package is a collection of related files and a
specification of the dependencies among them.
</p>
<p>
