Documentation/process: fix reST table border error

Fix reST error in Documentation/process/:

Documentation/process/2.Process.rst:131: ERROR: Malformed table.
Bottom/header table border does not match top border.

Fixes: 8962e40c ("docs: update kernel versions and dates in tables")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Tim Bird <tbird20d@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/2.Process.rst

@@ -134,7 +134,7 @@ and their maintainers are:
 	4.4	Greg Kroah-Hartman	(very long-term stable kernel)
 	4.9	Greg Kroah-Hartman
 	4.14	Greg Kroah-Hartman
-	======  ======================  ===========================
+	======  ======================  ==============================
 
 The selection of a kernel for long-term support is purely a matter of a
 maintainer having the need and the time to maintain that release.  There