Fixes drupal-composer#72: Require Composer API ^1.1.

Author: grasmash

composer.json

@@ -5,7 +5,7 @@
     "license": "GPL-2.0-or-later",
     "require": {
         "php": ">=5.4.5",
-        "composer-plugin-api": "^1.0.0",
+        "composer-plugin-api": "^1.1.0",
         "composer/semver": "^1.4"
     },
     "autoload": {