Build: Fix Sphinx version check

Older versions of sphinx-build print the version string
in a slightly different format. This made FindSphinx.cmake fail
to extract the version number and thus behave like Sphinx
was not installed.

This commit fixes the regexp to be less restrictive on
the message format.

Signed-off-by: Vikas Katariya <Vikas.Katariya@arm.com>
Change-Id: I2dd28e4fb4d693aee91eec9a8b138a43f5f2ebb3
1 file changed