[pkg] make sure we don't try to install elasticsearch 5.x

__pkginfo__.py

@@ -15,7 +15,7 @@
 
 __depends__ = {'cubicweb': '>= 3.22.2', 'six': '>= 1.4.0',
                'cwtags': None,
-               'elasticsearch': None,
+               'elasticsearch': '>=2.0.0,<3.0.0',
                'elasticsearch-dsl': None,
                'bs4': None,
 }