Ignore Vim's .swp files

**TLDR: Ignore Vim's hidden .swp files.**

***

**Long version:**
When you are editing a file in Vim, the program creates a hidden file ending with .swp in the same directory. That file exists until you stop editing the file in Vim. Annoying? Yes.

In Pattern Primer, this file shows up as a pattern:

![screen shot 2014-10-08 at 16 27 18](https://cloud.githubusercontent.com/assets/875708/4560858/4085c4c0-4ef8-11e4-902b-c4ee457352b6.png)

This pull request fixes the issue by checking that the file **ends** with ```.html``` not just **contains** ```.html```(as is the case with ```h1.html.swp```).