travis-ci: upgrade version number of nginx CORE, remove clang compiler mode from travis.

Author: xiaocang

.travis.yml

@@ -7,7 +7,6 @@ language: c
 
 compiler:
   - gcc
-  - clang
 
 addons:
   apt:
@@ -27,8 +26,8 @@ env:
     - JOBS=3
     - NGX_BUILD_JOBS=$JOBS
   matrix:
-    - NGINX_VERSION=1.11.2
     - NGINX_VERSION=1.19.3
+    - NGINX_VERSION=1.19.9
 
 services:
  - memcache