Update to be pq 7.0 compilant

pg singletons are no longer supported according to https://node-postgres.com/guides/upgrading , updated example to reflect upgrade changes.

README.md

@@ -20,10 +20,12 @@ If you're not familiar with the feature (I wasn't either) you can read this for
 ### pipe from a table to stdout
 
 ```js
-var pg = require('pg');
+var {Pool} = require('pg');
 var copyTo = require('pg-copy-streams').to;
 
-pg.connect(function(err, client, done) {
+var pool = new Pool();
+
+pool.connect(function(err, client, done) {
   var stream = client.query(copyTo('COPY my_table TO STDOUT'));
   stream.pipe(process.stdout);
   stream.on('end', done);
@@ -35,10 +37,12 @@ pg.connect(function(err, client, done) {
 
 ```js
 var fs = require('fs');
-var pg = require('pg');
+var {Pool} = require('pg');
 var copyFrom = require('pg-copy-streams').from;
 
-pg.connect(function(err, client, done) {
+var pool = new Pool();
+
+pool.connect(function(err, client, done) {
   var stream = client.query(copyFrom('COPY my_table FROM STDIN'));
   var fileStream = fs.createReadStream('some_file.tsv')
   fileStream.on('error', done);