fixed typo "downlaod"

Author: pkra

mathjax.rst

@@ -7,7 +7,7 @@ MathML that works in all modern browsers.  It was designed with the
 goal of consolidating the recent advances in web technologies into a
 single, definitive, math-on-the-web platform supporting the major
 browsers and operating systems.  It requires no setup on the part of
-the user (no plugins to downlaod or software to install), so the page
+the user (no plugins to download or software to install), so the page
 author can write web documents that include mathematics and be
 confident that users will be able to view it naturally and easily.
 One simply includes MathJax and some mathematics in a web page, and