feat(core): update to mongodb-core 3.1.2

Author: mbroadst

package.json

@@ -13,7 +13,7 @@
     "official"
   ],
   "dependencies": {
-    "mongodb-core": "3.1.1"
+    "mongodb-core": "3.1.2"
   },
   "devDependencies": {
     "bluebird": "3.5.0",