Modify URL of libpq documentation

When opening the URL in the browser the section about "Connection Strings" is directly displayed. This way there's no need to scroll to it. (Also use HTTPS)

config.example.yaml

@@ -19,7 +19,7 @@ clair:
     type: pgsql
     options:
       # PostgreSQL Connection string
-      # http://www.postgresql.org/docs/9.4/static/libpq-connect.html
+      # https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-CONNSTRING
       source:
 
       # Number of elements kept in the cache