Close <pre> tag in 1.1 example code

- In the 1.1-check-solarium-and-ping.php example code, the \<pre> tag is
  never closed after the var_dump. This fix closes the tag.

I added this because as a beginner, I pasted the code into my project just to test if solarium was configured properly. Since the \<pre> tag is never closed it broke the rest of the code on the page. I imagine other beginners do the same thing.