feat!: upgrade to stable (#1088)

* feat!: upgrade to stable

Author: sofisl

.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/debugger",
   "client_documentation": "https://cloud.google.com/nodejs/docs/reference/debug-agent/latest",
   "issue_tracker": "https://issuetracker.google.com/savedsearches/559771",
-  "release_level": "preview",
+  "release_level": "stable",
   "language": "nodejs",
   "repo": "googleapis/cloud-debug-nodejs",
   "distribution_name": "@google-cloud/debug-agent",

README.md

@@ -4,7 +4,7 @@
 
 # [Stackdriver Debugger: Node.js Client](https://github.com/googleapis/cloud-debug-nodejs)
 
-[![release level](https://img.shields.io/badge/release%20level-preview-yellow.svg?style=flat)](https://cloud.google.com/terms/launch-stages)
+[![release level](https://img.shields.io/badge/release%20level-stable-brightgreen.svg?style=flat)](https://cloud.google.com/terms/launch-stages)
 [![npm version](https://img.shields.io/npm/v/@google-cloud/debug-agent.svg)](https://www.npmjs.org/package/@google-cloud/debug-agent)
 
 
@@ -96,13 +96,14 @@ This library follows [Semantic Versioning](http://semver.org/).
 
 
 
+This library is considered to be **stable**. The code surface will not change in backwards-incompatible ways
+unless absolutely necessary (e.g. because of critical security issues) or with
+an extensive deprecation period. Issues and requests against **stable** libraries
+are addressed with the highest priority.
 
 
 
 
-This library is considered to be in **preview**. This means it is still a
-work-in-progress and under active development. Any release is subject to
-backwards-incompatible changes at any time.
 
 
 More Information: [Google Cloud Platform Launch Stages][launch_stages]