Update dependencies for koa 2 and async/await

package.json

@@ -21,12 +21,11 @@
   },
   "dependencies": {
     "addressparser": "^1.0.1",
-    "co": "^4.6.0",
-    "co-body": "^5.1.1",
     "config": "^1.20.4",
-    "koa": "^1.2.0",
-    "koa-router": "^5.4.0",
-    "koa-static": "^2.0.0",
+    "koa": "^2.3.0",
+    "koa-body": "^2.3.0",
+    "koa-router": "^7.2.1",
+    "koa-static": "^4.0.1",
     "mongodb": "^2.2.31",
     "nodemailer": "^2.4.2",
     "nodemailer-openpgp": "^1.0.2",
@@ -35,16 +34,14 @@
   },
   "devDependencies": {
     "chai": "^4.1.1",
-    "co-mocha": "^1.1.2",
     "eslint": "^4.4.1",
     "mocha": "^3.2.0",
-    "sinon": "^1.17.4",
+    "sinon": "^3.2.0",
     "supertest": "^3.0.0"
   },
   "greenkeeper": {
     "ignore": [
-      "nodemailer",
-      "sinon"
+      "nodemailer"
     ]
   }
 }