flow: Increase crit path routing iterations for strong_two_chains test

Can't reproduce failure of this test on TravisCI, but suspect it is
almost routable, so hopefully increasing the number of critical path
routing iterations will alleviate the failure.

Author: kmurray

vtr_flow/tasks/regression_tests/vtr_reg_strong/strong_two_chains/config/config.txt

@@ -24,4 +24,4 @@ qor_parse_file=qor_standard.txt
 pass_requirements_file=pass_requirements_chain.txt
 
 # Script parameters
-#script_params=
+script_params= -crit_path_router_iterations 75