add --pull to docker build

Author: neomantra

appveyor.yml

@@ -14,7 +14,7 @@ install:
 - ps: docker version
 
 build_script:
-- ps: docker build -t openresty:windows -f windows/Dockerfile .
+- ps: docker build --pull -t openresty:windows -f windows/Dockerfile .
 
 test_script:
 - cmd: docker run openresty:windows nginx -vt

docker_build_and_push_flavor.sh

@@ -17,7 +17,7 @@ DOCKER_BUILD_PARAMS="$@"
 
 cat /tmp/docker.pass | docker login -u="$DOCKER_USERNAME" --password-stdin
 
-docker build -t openresty:$FLAVOR -f $DOCKERFILE_PATH $DOCKER_BUILD_PARAMS .
+docker build --pull -t openresty:$FLAVOR -f $DOCKERFILE_PATH $DOCKER_BUILD_PARAMS .
 
 if [[ "$TRAVIS_BRANCH" == "master" ]] ; then
     cat /tmp/docker.pass | docker login -u="$DOCKER_USERNAME" --password-stdin &&