build/pkgs/sage_conf/src/sage_conf.py.in: replace subst by replace

Author: Matthias Koeppe

build/pkgs/sage_conf/src/sage_conf.py.in

@@ -18,7 +18,7 @@ NTL_LIBDIR = "@NTL_LIBDIR@"
 
 # Path to the ecl-config script
 # TODO: At the moment this is hard-coded, needs to be set during the configure phase if we want to support system-installed ecl.
-ECL_CONFIG = "${prefix}/bin/ecl-config".subst('${prefix}', SAGE_LOCAL)
+ECL_CONFIG = "${prefix}/bin/ecl-config".replace('${prefix}', SAGE_LOCAL)
 
 SAGE_NAUTY_BINS_PREFIX = "@SAGE_NAUTY_BINS_PREFIX@"