Update custom_signatures_export.py

Author: mkumykov

examples/custom_signatures_export.py

@@ -1,4 +1,4 @@
-#!/usr/local/bin/python2.7
+#!/usr/local/bin/python3
 # encoding: utf-8
 '''
 examples.custom_signatures_export -- Exports project scan data for projects that have custom signatures enabled
@@ -171,4 +171,4 @@ def main(argv=None): # IGNORE:C0111
         stats.print_stats()
         statsfile.close()
         sys.exit(0)
-    sys.exit(main())
+    sys.exit(main())