Update manifestformat for docker addon

src/addons.js

@@ -110,7 +110,7 @@ var KNOWN_ADDONS = {
         backup: NOOP,
         restore: NOOP
     },
-    _docker: {
+    docker: {
         setup: NOOP,
         teardown: NOOP,
         backup: NOOP,
@@ -219,7 +219,7 @@ function getBindsSync(app, addons) {
 
     for (let addon in addons) {
         switch (addon) {
-        case '_docker': binds.push('/var/run/docker.sock:/var/run/docker.sock:rw'); break;
+        case 'docker': binds.push('/var/run/docker.sock:/var/run/docker.sock:rw'); break;
         case 'localstorage':
             binds.push(path.join(paths.APPS_DATA_DIR, app.id, 'data') + ':/app/data:rw');
             if (!Array.isArray(addons[addon].bindMounts)) break;