Help: Fix version reference in 3.4 release notes

The 3.4 notes cover changes since 3.3, not 3.4.
diff --git a/Help/release/3.4.rst b/Help/release/3.4.rst
index 8cc0796..495391a 100644
--- a/Help/release/3.4.rst
+++ b/Help/release/3.4.rst
@@ -5,7 +5,7 @@
 
   .. contents::
 
-Changes made since CMake 3.4 include the following.
+Changes made since CMake 3.3 include the following.
 
 New Features
 ============