Actually update first-mate. Previous (51475fe231) updated atom-keymap.

Both were needed to introduce disposables, but I mixed up the commit
message in the previous commit.

package.json

@@ -28,7 +28,7 @@
     "delegato": "^1",
     "emissary": "^1.3.1",
     "event-kit": "0.7.2",
-    "first-mate": "^2.1.2",
+    "first-mate": "^2.2.0",
     "fs-plus": "^2.2.6",
     "fstream": "0.1.24",
     "fuzzaldrin": "^2.1",