Fix server restart test on Puma 3.12.1

Since puma/puma#1700, the default host is
correctly used. So `localhost` is used instead of `0.0.0.0`.

As a result, the log output on restart is changed, and the restart test
fails on Puma 3.12.1.
https://travis-ci.org/rails/rails/jobs/509239592#L2303-L2305

Specify binding explicitly to avoid being affected by Puma changes.

Gemfile.lock

@@ -347,8 +347,8 @@ GEM
     powerpack (0.1.1)
     psych (2.2.4)
     public_suffix (3.0.2)
-    puma (3.11.4)
-    puma (3.11.4-java)
+    puma (3.12.1)
+    puma (3.12.1-java)
     que (0.14.3)
     qunit-selenium (0.0.4)
       selenium-webdriver

railties/test/application/server_test.rb

@@ -44,13 +44,13 @@ def teardown
       pid = nil
 
       begin
-        pid = Process.spawn("#{app_path}/bin/rails server -P tmp/dummy.pid", in: slave, out: slave, err: slave)
+        pid = Process.spawn("#{app_path}/bin/rails server -b localhost -P tmp/dummy.pid", in: slave, out: slave, err: slave)
         assert_output("Listening", master)
 
         rails("restart")
 
         assert_output("Restarting", master)
-        assert_output("Inherited", master)
+        assert_output("tcp://localhost:3000", master)
       ensure
         kill(pid) if pid
       end