add 9.5-alpine to travis

Author: ncopa

.travis.yml

@@ -3,6 +3,7 @@ services: docker
 
 env:
   - VERSION=9.5
+  - VERSION=9.5 VARIANT=alpine
   - VERSION=9.4
   - VERSION=9.3
   - VERSION=9.2
@@ -13,8 +14,8 @@ install:
 
 before_script:
   - env | sort
-  - cd "$VERSION"
-  - image="postgres:$VERSION"
+  - cd "$VERSION/$VARIANT"
+  - image="postgres:${VERSION}${VARIANT:+-${VARIANT}}"
 
 script:
   - docker build -t "$image" .