Fix docker push for branches containing slashes, again

Author: Jamie Curnow

Jenkinsfile

@@ -10,11 +10,11 @@ pipeline {
 		IMAGE                      = "nginx-proxy-manager"
 		BUILD_VERSION              = getVersion()
 		MAJOR_VERSION              = "2"
-		COMPOSE_PROJECT_NAME       = "npm_${GIT_BRANCH}_${BUILD_NUMBER}"
+		BRANCH_LOWER               = "${BRANCH_NAME.toLowerCase().replaceAll('/', '-')}"
+		COMPOSE_PROJECT_NAME       = "npm_${BRANCH_LOWER}_${BUILD_NUMBER}"
 		COMPOSE_FILE               = 'docker/docker-compose.ci.yml'
 		COMPOSE_INTERACTIVE_NO_CLI = 1
 		BUILDX_NAME                = "${COMPOSE_PROJECT_NAME}"
-		BRANCH_LOWER               = "${BRANCH_NAME.toLowerCase().replaceAll('/', '-')}"
 	}
 	stages {
 		stage('Environment') {