scons: use python3-compatible lists

These changes were generated using python's `2to3` tool.

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
diff --git a/SConstruct b/SConstruct
index 0215aa8..a59a8ea 100644
--- a/SConstruct
+++ b/SConstruct
@@ -152,8 +152,7 @@
 except ImportError:
     pass
 else:
-    aliases = default_ans.keys()
-    aliases.sort()
+    aliases = sorted(default_ans.keys())
     env.Help('\n')
     env.Help('Recognized targets:\n')
     for alias in aliases: