inttest/rgen_1: double the timeout a second time

60s still seems to be too low, as it timed out for at least the R15B01
job of the timeout patch merge:
https://travis-ci.org/rebar/rebar/builds/15051701
https://travis-ci.org/rebar/rebar/jobs/15051703

inttest/rgen1/retest.config

@@ -1 +1 @@
-{timeout, 60000}.
+{timeout, 120000}.