Prepare 1.6.0 release

node_modules/@octokit/rest/lib/register-plugin.js

@@ -0,0 +1,7 @@
+module.exports = registerPlugin
+
+const factory = require('./factory')
+
+function registerPlugin (plugins, pluginFunction) {
+  return factory(plugins.includes(pluginFunction) ? plugins : plugins.concat(pluginFunction))
+}