Add missing period.

The "Import" section of the "Sass Basics" page was missing a period in the following sentence:

"When you import a file you don't need to include the file extension <code>.scss</code>"

It should read:

"When you import a file you don't need to include the file extension <code>.scss</code>."
Merge pull request #73 from edull24/master

Add missing period.