Honour SOURCE_DATE_EPOCH for VERSION default

Merged upstream as cd3f1024a37a332f1d4fa96a817ca80dfa2a478c, but not yet in a
release. GitHub PR: https://github.com/kichik/nsis/pull/13

Python snippet from: https://reproducible-builds.org/docs/source-date-epoch/#python


diff --git a/SConstruct b/SConstruct
index e8252c9..41786f2 100755
--- a/SConstruct
+++ b/SConstruct
@@ -95,8 +95,8 @@ default_doctype = 'html'
 if defenv.WhereIs('hhc', os.environ['PATH']):
 	default_doctype = 'chm'
 
-from time import strftime, gmtime
-cvs_version = strftime('%d-%b-%Y.cvs', gmtime())
+import time
+cvs_version = time.strftime('%d-%b-%Y.cvs', time.gmtime(int(os.environ.get('SOURCE_DATE_EPOCH', time.time()))))
 
 opts = Variables()