[releng] convert-to-tarballs: fix error when printing versions

[Michael Catanzaro <mcatanzaro src gnome org>]

commit a90d7477bdae4d7ead09cdb7097a2047caa56aeb
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Mon Feb 17 18:23:42 2020 -0600

    convert-to-tarballs: fix error when printing versions
    
    I broke this in the python3 port.

 tools/smoketesting/convert-to-tarballs.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/tools/smoketesting/convert-to-tarballs.py b/tools/smoketesting/convert-to-tarballs.py
index ee319d1..d7c03cf 100755
--- a/tools/smoketesting/convert-to-tarballs.py
+++ b/tools/smoketesting/convert-to-tarballs.py
@@ -740,7 +740,7 @@ class ConvertToTarballs:
         for idx in range(len(self.options.release_sets)):
             release_set = self.options.release_sets[idx]
             if release_set != 'Other':
-                versions.write('## %s\n' % string.upper(release_set))
+                versions.write('## %s\n' % release_set.upper())
                 modules_sorted = self.options.release_set[idx]
                 modules_sorted.sort()
                 subdirs = {}