THRIFT-2874: C++ - typo in TDenseProtocol comment fixed

Client: C++
Patch: Nobuaki Sukegawa

This closes #302
diff --git a/lib/cpp/src/thrift/protocol/TDenseProtocol.h b/lib/cpp/src/thrift/protocol/TDenseProtocol.h
index e7f2cd2..d7a119a 100644
--- a/lib/cpp/src/thrift/protocol/TDenseProtocol.h
+++ b/lib/cpp/src/thrift/protocol/TDenseProtocol.h
@@ -54,7 +54,7 @@
  * TODO(dreiss): New class write with old meta.
  *
  * We override all of TBinaryProtocol's methods.
- * We inherit so that we can can explicitly call TBPs's primitive-writing
+ * We inherit so that we can explicitly call TBPs's primitive-writing
  * methods within our versions.
  *
  */