tests: upgrade nginx to 1.25.1.

Author: zhuizhuhaomeng

.travis.yml

@@ -1,5 +1,5 @@
 sudo: required
-dist: bionic
+dist: focal 
 
 os: linux
 
@@ -27,8 +27,8 @@ env:
     - LD_LIBRARY_PATH=$LUAJIT_LIB:$LD_LIBRARY_PATH
     - TEST_NGINX_SLEEP=0.006
   matrix:
-    - NGINX_VERSION=1.21.4 OPENSSL_VER=1.1.0l
-    - NGINX_VERSION=1.21.4 OPENSSL_VER=1.1.1l
+    - NGINX_VERSION=1.25.1 OPENSSL_VER=1.1.0l
+    - NGINX_VERSION=1.25.1 OPENSSL_VER=1.1.1l
 
 install:
   - if [ ! -d download-cache ]; then mkdir download-cache; fi