[clang][www] Fix typo. NFC

Fix a one letter typo in diagnostics.html. (Wanted to try it with
arcanist).

Patch by king6cong

Differential Revision: https://reviews.llvm.org/D52511

llvm-svn: 343372

clang/www/diagnostics.html

@@ -292,7 +292,7 @@ implements the "wwopen" class of APIs):</p>
 </pre>
 
 <p>In practice, we've found that Clang's treatment of macros is actually more useful in multiply nested
-macros that in simple ones.</p>
+macros than in simple ones.</p>
 
 <h2>Quality of Implementation and Attention to Detail</h2>