feat: upgrade dependencies

BREAKING CHANGE:
This could break your code bc of the nano upgrade to v9 (via nano-option). Please refer to [nano documentation](https://github.com/apache/couchdb-nano/).

Updated packages:
* async              ^2.6.0  →    ^3.2.0
* couchdb-compile   ^1.10.0  →   ^1.11.0
* nano-option        ^1.3.0  →    ^2.0.0
* nano               ^6.4.3  →    ^9.0.3
* standard          ^11.0.0  →   ^16.0.3
* tap              ^14.10.7  →  ^14.11.0

cli.js

@@ -1,15 +1,15 @@
 #!/usr/bin/env node
 
-var configure = require('./')
+const configure = require('./')
 
-var args = process.argv.slice(2)
+const args = process.argv.slice(2)
 if (!args.length) {
   console.log('Usage: \ncouchdb-configure URL [SOURCE]')
   process.exit()
 }
 
-var url = args[0]
-var source = args[1] || process.cwd()
+const url = args[0]
+const source = args[1] || process.cwd()
 
 configure(url, source, function (error, response) {
   if (error) return console.error(error)

index.js

@@ -1,10 +1,10 @@
-var nanoOption = require('nano-option')
-var async = require('async')
-var compile = require('couchdb-compile')
-var assert = require('assert')
+const nanoOption = require('nano-option')
+const async = require('async')
+const compile = require('couchdb-compile')
+const assert = require('assert')
 
 module.exports = function configure (url, source, callback) {
-  var couch = nanoOption(url)
+  const couch = nanoOption(url)
 
   assert(typeof couch.request === 'function',
     'URL must point to the root of a CouchDB server (not to a database).')
@@ -22,11 +22,11 @@ module.exports = function configure (url, source, callback) {
           async.waterfall([
             compile.bind(null, source, { index: true }),
             (config, done) => {
-              var settings = Object.keys(config)
+              const settings = Object.keys(config)
                 .reduce(function (memo, key) {
                   if (typeof config[key] !== 'object') return memo
 
-                  var section = Object.keys(config[key])
+                  const section = Object.keys(config[key])
                     .map(function (k) {
                       return {
                         path: encodeURIComponent(key) + '/' + encodeURIComponent(k),
@@ -42,7 +42,7 @@ module.exports = function configure (url, source, callback) {
         }
       ], done)
     },
-    ([ version, settings ], done) => {
+    ([version, settings], done) => {
       function writeConfig (configPath, done) {
         async.map(settings, (setting, done) => {
           couch.request({
@@ -76,7 +76,7 @@ module.exports = function configure (url, source, callback) {
       }
     },
     (responses, done) => {
-      var response = responses.reduce(function (memo, response) {
+      const response = responses.reduce(function (memo, response) {
         memo[response.path] = {
           ok: true,
           value: response.value