update downloads badge and travis config

.travis.yml

@@ -1,10 +1,10 @@
 language: node_js
 node_js:
-  - "6"
   - "8"
   - "10"
   - "12"
+  - "14"
 script:
   - npm run eslint
   - npm run test
-after_success: 'npm run coveralls'
+after_success: 'npm run coveralls'

README.md

@@ -1,7 +1,7 @@
 [![Build Status](https://travis-ci.org/animir/node-rate-limiter-flexible.png)](https://travis-ci.org/animir/node-rate-limiter-flexible)
 [![Coverage Status](https://coveralls.io/repos/animir/node-rate-limiter-flexible/badge.svg?branch=master)](https://coveralls.io/r/animir/node-rate-limiter-flexible?branch=master)
 [![npm version](https://badge.fury.io/js/rate-limiter-flexible.svg)](https://www.npmjs.com/package/rate-limiter-flexible)
-![npm](https://img.shields.io/npm/dt/rate-limiter-flexible.svg)
+![npm](https://img.shields.io/npm/dm/rate-limiter-flexible.svg)
 [![node version][node-image]][node-url]
 [![deno version](https://img.shields.io/badge/deno-^1.5.3-lightgrey?logo=deno)](https://github.com/denoland/deno)