doc: modernize and fix code examples in https.md

* Replace `var` by `const`.
* Comment out ellipses.
* Update code example (provide relevant file path, add missing option).
PR-URL: #12171
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: vsemozhetbyt

doc/api/https.md

@@ -69,7 +69,8 @@ const https = require('https');
 constfs=require('fs');
 
 constoptions= {
- pfx:fs.readFileSync('server.pfx')
+ pfx:fs.readFileSync('test/fixtures/test_cert.pfx'),
+ passphrase:'sample'
 };
 
 https.createServer(options, (req, res) => {
@@ -143,14 +144,14 @@ Example:
 ```js
 consthttps=require('https');
 
-var options = {
+constoptions= {
  hostname:'encrypted.google.com',
  port:443,
  path:'/',
  method:'GET'
 };
 
-var req =https.request(options, (res) => {
+constreq=https.request(options, (res) => {
 console.log('statusCode:', res.statusCode);
 console.log('headers:', res.headers);
 
@@ -218,7 +219,7 @@ In order to specify these options, use a custom [`Agent`][].
 Example:
 
 ```js
-var options = {
+constoptions= {
  hostname:'encrypted.google.com',
  port:443,
  path:'/',
@@ -228,8 +229,8 @@ var options = {
 };
 options.agent=newhttps.Agent(options);
 
-var req =https.request(options, (res) => {
-...
+constreq=https.request(options, (res) => {
+//...
 });
 ```
 
@@ -238,7 +239,7 @@ Alternatively, opt out of connection pooling by not using an `Agent`.
 Example:
 
 ```js
-var options = {
+constoptions= {
  hostname:'encrypted.google.com',
  port:443,
  path:'/',
@@ -248,8 +249,8 @@ var options = {
  agent:false
 };
 
-var req =https.request(options, (res) => {
-...
+constreq=https.request(options, (res) => {
+//...
 });
 ```