docs: fix the URL regex (#1057)

The "//[host][:port][/database]" portion of the URL regex does not accurately represent the URL variations that are actually accepted.
The proposed "[//host[:port]/][database]" does.

README.md

@@ -93,7 +93,7 @@ jdbc:postgresql://host:port/
```
The general format for a JDBC URL for connecting to a PostgreSQL server is as follows, with items in square brackets ([ ]) being optional:
```
jdbc:postgresql://[host][:port][/[database]][?property1=value1[&property2=value2]...]
jdbc:postgresql:[//host[:port]/][database][?property1=value1[&property2=value2]...]
```
where:
 * **jdbc:postgresql:** (Required) is known as the sub-protocol and is constant.