Use Arial as default font.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@52197 91177308-0d34-0410-b5e6-96231b3b80d8

www/content.css

@@ -1,7 +1,7 @@
 html, body {
 	padding:0px;	
 	color:#000000; background-color:#ffffff;
-  font-family: Helvetica, sans-serif;
+  font-family: Arial, sans-serif;
 }
 
 /* Slides */