Add extra version of py-werkzeug (#15115)

var/spack/repos/builtin/packages/py-werkzeug/package.py

@@ -13,6 +13,7 @@ class PyWerkzeug(PythonPackage):
     url      = "https://pypi.io/packages/source/W/Werkzeug/Werkzeug-0.16.0.tar.gz"
 
     version('0.16.0',  sha256='7280924747b5733b246fe23972186c6b348f9ae29724135a6dfc1e53cea433e7')
+    version('0.15.4',  sha256='a0b915f0815982fb2a09161cb8f31708052d0951c3ba433ccc5e1aa276507ca6')
     version('0.11.15', sha256='455d7798ac263266dbd38d4841f7534dd35ca9c3da4a8df303f8488f38f3bcc0')
     version('0.11.11', sha256='e72c46bc14405cba7a26bd2ce28df734471bc9016bc8b4cb69466c2c14c2f7e5')