add composer post-install-cmd script which deletes the cache directory after installation

.dockerignore

@@ -0,0 +1,3 @@
+.git
+var/*
+vendor/*

composer.json

@@ -121,6 +121,9 @@
 		],
 		"post-autoload-dump": [
 			"@typo3-cms-scripts"
+		],
+		"post-install-cmd": [
+			"rm -rf /var/www/html/var/cache/*"
 		]
 	}
 }