Remove Node.js v8 support (#1402)

docs/examples/asStream.asciidoc

@@ -57,7 +57,7 @@ async function run () {
   })
 
   // stream async iteration, available in Node.js ≥ 10
-  var payload = ''
+  let payload = ''
   body.setEncoding('utf8')
   for await (const chunk of body) {
     payload += chunk
@@ -65,7 +65,7 @@ async function run () {
   console.log(JSON.parse(payload))
 
   // classic stream callback style
-  var payload = ''
+  let payload = ''
   body.setEncoding('utf8')
   body.on('data', chunk => { payload += chunk })
   body.on('error', console.log)
@@ -101,4 +101,4 @@ fastify.post('/search/:index', async (req, reply) => {
 })
 
 fastify.listen(3000)
-----
+----

docs/examples/scroll.asciidoc

@@ -124,7 +124,7 @@ const client = new Client({ node: 'http://localhost:9200' })
 
 // Scroll utility
 async function * scrollSearch (params) {
-  var response = await client.search(params)
+  let response = await client.search(params)
 
   while (true) {
     const sourceHits = response.body.hits.hits
@@ -190,4 +190,4 @@ async function run () {
 }
 
 run().catch(console.log)
-----
+----

docs/examples/sql.query.asciidoc

@@ -58,7 +58,7 @@ async function run () {
 
   const data = body.rows.map(row => {
     const obj = {}
-    for (var i = 0; i < row.length; i++) {
+    for (let i = 0; i < row.length; i++) {
       obj[body.columns[i].name] = row[i]
     }
     return obj