travis-ci: upgraded openssl to 1.1.1k.

Author: xiaocang

.travis.yml

@@ -39,7 +39,7 @@ env:
     - NGINX_VERSION=1.17.8 OPENSSL_VER=1.0.2u
     - NGINX_VERSION=1.19.9 OPENSSL_VER=1.0.2u
     - NGINX_VERSION=1.19.9 OPENSSL_VER=1.1.0l
-    - NGINX_VERSION=1.19.9 OPENSSL_VER=1.1.1f
+    - NGINX_VERSION=1.19.9 OPENSSL_VER=1.1.1k
 
 services:
  - memcache