Drop alpine 3.8 and jessie builds; these were only kept around for us…

…ers to transition to stretch or 3.9 (see docker-library/php#504)

.travis.yml

@@ -16,33 +16,20 @@ env:
   - VERSION=7.3 VARIANT=alpine3.9/cli
   - VERSION=7.3 VARIANT=alpine3.9/fpm
   - VERSION=7.3 VARIANT=alpine3.9/zts
-  - VERSION=7.3 VARIANT=alpine3.8/cli
-  - VERSION=7.3 VARIANT=alpine3.8/fpm
-  - VERSION=7.3 VARIANT=alpine3.8/zts
   - VERSION=7.2 VARIANT=stretch/cli
   - VERSION=7.2 VARIANT=stretch/apache
   - VERSION=7.2 VARIANT=stretch/fpm
   - VERSION=7.2 VARIANT=stretch/zts
   - VERSION=7.2 VARIANT=alpine3.9/cli
   - VERSION=7.2 VARIANT=alpine3.9/fpm
   - VERSION=7.2 VARIANT=alpine3.9/zts
-  - VERSION=7.2 VARIANT=alpine3.8/cli
-  - VERSION=7.2 VARIANT=alpine3.8/fpm
-  - VERSION=7.2 VARIANT=alpine3.8/zts
   - VERSION=7.1 VARIANT=stretch/cli
   - VERSION=7.1 VARIANT=stretch/apache
   - VERSION=7.1 VARIANT=stretch/fpm
   - VERSION=7.1 VARIANT=stretch/zts
-  - VERSION=7.1 VARIANT=jessie/cli
-  - VERSION=7.1 VARIANT=jessie/apache
-  - VERSION=7.1 VARIANT=jessie/fpm
-  - VERSION=7.1 VARIANT=jessie/zts
   - VERSION=7.1 VARIANT=alpine3.9/cli
   - VERSION=7.1 VARIANT=alpine3.9/fpm
   - VERSION=7.1 VARIANT=alpine3.9/zts
-  - VERSION=7.1 VARIANT=alpine3.8/cli
-  - VERSION=7.1 VARIANT=alpine3.8/fpm
-  - VERSION=7.1 VARIANT=alpine3.8/zts
 
 install:
   - git clone https://github.com/docker-library/official-images.git ~/official-images