Extract the Sphinx version components

The version pattern lacked capture groups, so the major, minor and patch
components of the Sphinx version were always empty.

Capture each component.

Change-Id: I5c333360986aa831e9a665947483abd389bc76dd

cmake/FindSphinx.cmake

diff --git a/cmake/FindSphinx.cmake b/cmake/FindSphinx.cmake
index 085b72a..2fdf7e9 100644
--- a/cmake/FindSphinx.cmake
+++ b/cmake/FindSphinx.cmake
@@ -68,12 +68,12 @@
     string (REGEX REPLACE "^sphinx-build[ \t]+([^ \t]+)$" "\\1" Sphinx_VERSION
       "${_Sphinx_VERSION_STRING}")
 
-    if (Sphinx_VERSION MATCHES "[0-9]+\\.[0-9]+\\.[0-9]+")
+    if (Sphinx_VERSION MATCHES "^([0-9]+)\\.([0-9]+)\\.([0-9]+)")
       set (Sphinx_VERSION_COMPONENTS 3)
       set (Sphinx_VERSION_MAJOR ${CMAKE_MATCH_1})
       set (Sphinx_VERSION_MINOR ${CMAKE_MATCH_2})
       set (Sphinx_VERSION_PATCH ${CMAKE_MATCH_3})
-    endif (Sphinx_VERSION MATCHES "[0-9]+\\.[0-9]+\\.[0-9]+")
+    endif (Sphinx_VERSION MATCHES "^([0-9]+)\\.([0-9]+)\\.([0-9]+)")
   else (_Sphinx_BUILD_RESULT EQUAL 0)
     message (WARNING "Could not determine sphinx-build version: ${_Sphinx_BUILD_ERROR}")
   endif (_Sphinx_BUILD_RESULT EQUAL 0)