Merge pull request #6 from samcv/license

Use SPDX identifier in license field of META6.json

META6.json

@@ -7,6 +7,6 @@
     "provides": {
         "Text::Markov" : "lib/Text/Markov.pm"
     },
-    "license" : "http://www.perlfoundation.org/artistic_license_2_0",
+    "license" : "Artistic-2.0",
     "source-url": "git://github.com/bbkr/text_markov.git"
 }