[package.json] Add a jspm field to make CodeMirror installable with that tool

package.json

@@ -19,5 +19,10 @@
                     "email": "marijnh@gmail.com",
                     "web": "http://marijnhaverbeke.nl"}],
     "repository": {"type": "git",
-                   "url": "https://github.com/codemirror/CodeMirror.git"}
+                   "url": "https://github.com/codemirror/CodeMirror.git"},
+    "jspm": {
+      "directories": {},
+      "dependencies": {},
+      "devDependencies": {}
+    }
 }