Update askForUsageDataPermission to use inquirer

Prompt's dependency winston is causing a warning in the console:

> (node:15613) Warning: Accessing non-existent property 'padLevels' of module exports inside circular dependency

This has been raised as an issue on prompt's GitHub repo [1] but given the last release of prompt was 4 years ago, I think it makes sense to move away to an alternative that's actively maintained.

[1]: flatiron/prompt#199

lib/usage-data-prompt.txt

@@ -6,4 +6,4 @@ With your permission, the kit can send useful anonymous usage data
 for analysis to help the team improve the service. Read more here:
 https://govuk-prototype-kit.herokuapp.com/docs/usage-data
 
-Do you give permission for the kit to send anonymous usage data? (y/n)
+Do you give permission for the kit to send anonymous usage data?

lib/usage_data.js

@@ -4,7 +4,7 @@ const fs = require('fs')
 const os = require('os')
 
 // NPM dependencies
-const prompt = require('prompt')
+const inquirer = require('inquirer')
 const universalAnalytics = require('universal-analytics')
 const uuidv4 = require('uuid/v4')
 
@@ -37,34 +37,15 @@ exports.setUsageDataConfig = function (usageDataConfig) {
 // returns a Promise with the user's answer
 exports.askForUsageDataPermission = function () {
   return new Promise(function (resolve, reject) {
-    // Set up prompt settings
-    prompt.colors = false
-    prompt.start()
-    prompt.message = ''
-    prompt.delimiter = ''
+    const description = fs.readFileSync(path.join(__dirname, 'usage-data-prompt.txt'), 'utf8').trim()
 
-    const description = fs.readFileSync(path.join(__dirname, 'usage-data-prompt.txt'), 'utf8')
-
-    prompt.get([{
-      name: 'answer',
-      description: description,
-      required: true,
-      type: 'string',
-      pattern: /y(es)?|no?/i,
-      message: 'Please enter y or n',
-      ask: function () {
-        return process.stdout.isTTY
-      }
-    }], function (err, result) {
-      if (err) {
-        reject(err)
-      }
-      if (result.answer.match(/y(es)?/i)) {
-        resolve('yes')
-      } else {
-        resolve('no')
-      }
-    })
+    inquirer.prompt([{
+      name: 'usageData',
+      message: description,
+      type: 'confirm',
+      when: () => process.stdout.isTTY,
+      default: false
+    }]).then(answers => resolve(answers.usageData))
   })
 }
 

start.js

@@ -13,17 +13,14 @@ const usageDataConfig = usageData.getUsageDataConfig()
 if (usageDataConfig.collectUsageData === undefined) {
   // No recorded answer, so ask for permission
   const promptPromise = usageData.askForUsageDataPermission()
-  promptPromise.then(function (answer) {
-    if (answer === 'yes') {
-      usageDataConfig.collectUsageData = true
-      usageData.setUsageDataConfig(usageDataConfig)
+  promptPromise.then(function (permissionGranted) {
+    usageDataConfig.collectUsageData = permissionGranted
+    usageData.setUsageDataConfig(usageDataConfig)
+
+    if (permissionGranted) {
       usageData.startTracking(usageDataConfig)
-    } else if (answer === 'no') {
-      usageDataConfig.collectUsageData = false
-      usageData.setUsageDataConfig(usageDataConfig)
-    } else {
-      console.error(answer)
     }
+
     runGulp()
   })
 } else if (usageDataConfig.collectUsageData === true) {