feat: promote to 1.0.0 (#167)

Release-As: 1.0.0

.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/dns",
   "client_documentation": "https://googleapis.dev/java/google-cloud-clients/latest/index.html?com/google/cloud/dns/package-summary.html",
   "issue_tracker": "https://issuetracker.google.com/savedsearches/559772",
-  "release_level": "alpha",
+  "release_level": "ga",
   "language": "java",
   "repo": "googleapis/java-dns",
   "repo_short": "java-dns",

README.md

@@ -10,9 +10,6 @@ Java idiomatic client for [Google Cloud DNS][cloud-dns].
 - [Product Documentation][dns-product-docs]
 - [Client Library Documentation][dns-client-lib-docs]
 
-> Note: This client is a work-in-progress, and may occasionally
-> make backwards-incompatible changes.
-
 Quickstart
 ----------
 If you are using Maven with a BOM, add this to your pom.xml file.
@@ -382,10 +379,6 @@ Versioning
 
 This library follows [Semantic Versioning](http://semver.org/).
 
-It is currently in major version zero (``0.y.z``), which means that anything
-may change at any time and the public API should not be considered
-stable.
-
 Contributing
 ------------