Tests: fix expect-100-continue for 0.7.31.

In nginx 0.7.31 processing of "Expect" header only happens while actually
reading request body.  Add proxy_pass as it always reads request body.

expect-100-continue.t

diff --git a/expect-100-continue.t b/expect-100-continue.t
index 9ef0e52..cf0f9c5 100644
--- a/expect-100-continue.t
+++ b/expect-100-continue.t
@@ -43,6 +43,11 @@
     server {
         listen       127.0.0.1:8080;
         server_name  localhost;
+        location / {
+            proxy_pass http://localhost:8080/local;
+        }
+        location /local {
+        }
     }
 }