Help/dev: Update source code guide to specify clang-format version 15

Help/dev/source.rst

@@ -9,7 +9,7 @@ See documentation on `CMake Development`_ for more information.
 C++ Code Style
 ==============
 
-We use `clang-format`_ version **6.0** to define our style for C++ code in
+We use `clang-format`_ version **15** to define our style for C++ code in
 the CMake source tree.  See the `.clang-format`_ configuration file for our
 style settings.  Use the `Utilities/Scripts/clang-format.bash`_ script to
 format source code.  It automatically runs ``clang-format`` on the set of