- fix typo in thrift whitepaper

Summary:
clases -> classes

Reviewed By: scott m


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665088 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/doc/thrift.tex b/doc/thrift.tex
index b0838f4..fc1e6ba 100644
--- a/doc/thrift.tex
+++ b/doc/thrift.tex
@@ -852,7 +852,7 @@
 creation and destruction issues, while the \texttt{Runnable} implementation deals
 with the application-specific per-thread logic. The benefit of this approach
 is that developers can easily subclass the Runnable class without pulling in 
-platform-specific super-clases.
+platform-specific super-classes.
 
 \subsection{Thread, Runnable, and shared\_ptr}
 We use \texttt{boost::shared\_ptr} throughout the \texttt{ThreadManager} and