fix(http): make ace-http command executable

According to https://docs.npmjs.com/files/package.json#bin, this should
be sufficient.

Still needs testing.

Addresses #51

src/http/http.js

@@ -1,3 +1,5 @@
+#!/usr/bin/env node
+
 const express = require('express');
 const uuidv4 = require('uuid/v4');
 const multer = require('multer');