Use rm -rf to delete composer lock file so it wont error if missing (#71)

Author: weitzman

commands/web/poser

@@ -10,5 +10,6 @@
 export COMPOSER=composer.contrib.json
 .ddev/commands/web/expand-composer-json "$DDEV_PROJECT_NAME"
 composer install
-rm composer.contrib.json composer.contrib.lock
+# The -f flag suppresses errors if lock file does not exist.
+rm -f composer.contrib.json composer.contrib.lock
 touch $DDEV_DOCROOT/core/.env