Fix example for the 'var' element.

From http://reference.sitepoint.com/html/var:
  The var element is used to indicate that the text is a variable and
  shouldn’t be taken literally. Instead, it’s an example that should be
  replaced with your own value.

Also in
http://articles.sitepoint.com/article/html-37-steps-perfect-markup/2 at
item 29.:
  A common misconception is that var should be used for marking up
  variables in programming code samples.