Update link to libpq-envvars documentation

Fixes link to avoid extra redirect and additionally link to the documentation for the current version instead of a fixed version (10)

postgres/content.md

@@ -57,7 +57,7 @@ This environment variable is required for you to use the PostgreSQL image. It mu
 
 **Note 1:** The PostgreSQL image sets up `trust` authentication locally so you may notice a password is not required when connecting from `localhost` (inside the same container). However, a password will be required if connecting from a different host/container.
 
-**Note 2:** This variable defines the superuser password in the PostgreSQL instance, as set by the `initdb` script during initial container startup. It has no effect on the `PGPASSWORD` environment variable that may be used by the `psql` client at runtime, as described at [https://www.postgresql.org/docs/10/static/libpq-envars.html](https://www.postgresql.org/docs/10/static/libpq-envars.html). `PGPASSWORD`, if used, will be specified as a separate environment variable.
+**Note 2:** This variable defines the superuser password in the PostgreSQL instance, as set by the `initdb` script during initial container startup. It has no effect on the `PGPASSWORD` environment variable that may be used by the `psql` client at runtime, as described at [https://www.postgresql.org/docs/current/libpq-envars.html](https://www.postgresql.org/docs/current/libpq-envars.html). `PGPASSWORD`, if used, will be specified as a separate environment variable.
 
 ### `POSTGRES_USER`