fix(packagist): use static endpoint for org lookups

Closes #2785

lib/datasource/packagist.js

@@ -173,12 +173,15 @@ async function getAllPackages(regUrl) {
 
 async function packagistOrgLookup(name) {
   const regUrl = 'https://packagist.org';
-  const pkgUrl = URL.resolve(regUrl, `/packages/${name}.json`);
+  const pkgUrl = URL.resolve(regUrl, `/p/${name}.json`);
   const res = (await got(pkgUrl, {
     json: true,
     retry: 5,
-  })).body.package;
-  const dep = extractDepReleases(res.versions);
+  })).body.packages[name];
+  if (!res) {
+    return null;
+  }
+  const dep = extractDepReleases(res);
   dep.name = name;
   logger.trace({ dep }, 'dep');
   return dep;