Drop bluebird dependency, use native Promise

Node.js provides native Promise API for more than six years. Node.js
versions older than that are unmaintained and unsupported for many
years. Thus Bluebird dependency is completely unnecessary.

Resolves alvarcarto#159

Author: jirutka

package-lock.json

@@ -22,7 +22,6 @@
   },
   "homepage": "https://github.com/alvarcarto/url-to-pdf-api#readme",
   "dependencies": {
-    "bluebird": "^3.5.0",
     "body-parser": "^1.18.2",
     "compression": "^1.7.1",
     "cors": "^2.8.4",

package.json

@@ -1,14 +1,8 @@
 const createApp = require('./app');
 const enableDestroy = require('server-destroy');
-const BPromise = require('bluebird');
 const logger = require('./util/logger')(__filename);
 const config = require('./config');
 
-BPromise.config({
-  warnings: config.NODE_ENV !== 'production',
-  longStackTraces: true,
-});
-
 const app = createApp();
 const server = app.listen(config.PORT, () => {
   logger.info(

src/index.js

@@ -1,5 +1,4 @@
 const _ = require('lodash');
-const BPromise = require('bluebird');
 
 // Route which assumes that the Promise `func` returns, will be resolved
 // with data which will be sent as json response.
@@ -28,7 +27,7 @@ function createRoute(func, responseHandler) {
       let valuePromise = callback();
       if (!_.isFunction(_.get(valuePromise, 'then'))) {
         // It was a not a Promise, so wrap it as a Promise
-        valuePromise = BPromise.resolve(valuePromise);
+        valuePromise = Promise.resolve(valuePromise);
       }
 
       if (_.isFunction(responseHandler)) {

src/util/express.js

@@ -3,17 +3,12 @@
 const chai = require('chai');
 const fs = require('fs');
 const request = require('supertest');
-const BPromise = require('bluebird');
 const { getResource } = require('./util');
 const pdf = require('pdf-parse');
 const createApp = require('../src/app');
 
 const DEBUG = false;
 
-BPromise.config({
-  longStackTraces: true,
-});
-
 const app = createApp();
 
 function normalisePdfText(text) {