DOC: Use HTTPS URL in docs.

Author: wouterbeek

README.md

@@ -13,7 +13,7 @@ dnf install graphviz # Fedora, Red Hat
 
 ## Installation
 
-Run the following in [SWI-Prolog](http://www.swipl-prolog.org):
+Run the following in [SWI-Prolog](https://www.swipl-prolog.org):
 
 ```pl
 pack_install(prolog_graphviz).

test/test_graph_export.pl renamed to test/test_graphviz.pl

@@ -1,5 +1,3 @@
-:- begin_tests(gv).
-
 :- use_module(library(apply)).
 :- use_module(library(plunit)).
 :- use_module(library(process)).
@@ -12,9 +10,7 @@
     test_gv_export(+, 1),
     test_gv_export(+, 1, +).
 
-
-
-
+:- begin_tests(gv).
 
 test(hello, [cleanup(delete_file(File))]) :-
   File = 'hello.pdf',