doc: update robots.txt exclusion list

Developers using google search can accidentally find older versions of
documents and lead to confusion.  While we do maintain previous release
documentation on the site, we should have a preference for the latest
documentation when using external search engines.  (Note the on-site
search always returns version-specific results.)

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/scripts/publish-robots.txt

@@ -8,3 +8,9 @@ Disallow: /0.5/
 Disallow: /0.6/
 Disallow: /0.7/
 Disallow: /0.8/
+Disallow: /1.0/
+Disallow: /1.1/
+Disallow: /1.2/
+Disallow: /1.3/
+Disallow: /1.4/
+Disallow: /1.5/