PGPORT environment variable must be set for scribevulnpolicy to work

Following the instructions in the SVP README, the scribevulnpolicy tool is not able to query the Clair database.  I encountered the following:

```
$ ./scribevulnpolicy -V
error retrieving platforms: dial tcp: lookup tcp/sslmode=disable: nodename nor servname provided, or not known
```

Fortunately, setting the `PGPORT` environment variable fixed this issue.

```
export PGPORT=5432
```