travis-ci: bump the NGINX core to 1.19.9, remove clang compiler mode from travis to save credits. (openresty#92)

Author: xiaocang

.travis.yml

@@ -11,7 +11,6 @@ cache:
 
 compiler:
   - gcc
-  - clang
 
 env:
   global:
@@ -24,8 +23,8 @@ env:
     - JOBS=3
     - NGX_BUILD_JOBS=$JOBS
   matrix:
-    - NGINX_VERSION=1.11.2
-    - NGINX_VERSION=1.19.3
+    - NGINX_VERSION=1.17.8
+    - NGINX_VERSION=1.19.9
 
 services:
  - memcache