polyfill Promise with bluebird

fixes: Uncaught TypeError: Promise.defer is not a function - adds bluebird

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ex-mode",
   "main": "./lib/ex-mode",
-  "version": "0.10.0",
+  "version": "0.10.1",
   "description": "Ex for Atom's vim-mode",
   "activationCommands": {
     "atom-workspace": "ex-mode:open"
@@ -12,11 +12,12 @@
     "atom": ">=0.200.0 <2.0.0"
   },
   "dependencies": {
-    "underscore-plus": "1.x",
-    "event-kit": "^0.7.2",
-    "space-pen": "^5.1.1",
     "atom-space-pen-views": "^2.0.4",
-    "fs-plus": "^2.2.8"
+    "bluebird": "^3.4.1",
+    "event-kit": "^0.7.2",
+    "fs-plus": "^2.2.8",
+    "space-pen": "^5.1.1",
+    "underscore-plus": "1.x"
   },
   "consumedServices": {
     "vim-mode": {