Print github-specific deprecation notice on GH.

bin/legacy/deprecation.js

@@ -1,9 +1,19 @@
 const winston = require('winston');
 
-// deprecationNotice adds middleware to the yargs chain to display a deprecation notice.
-const deprecationNotice = (opts = {}) => {
+// addDeprecationNotice adds middleware to the yargs chain to display a deprecation notice.
+const addDeprecationNotice = (opts = {}) => {
   const { builder, notice } = opts;
-  return (yargs) => builder(yargs).middleware([(argv) => winston.warn(notice)]);
+  return (yargs) =>
+    builder(yargs).middleware([(opts) => deprecationNotice(opts, notice)]);
 };
 
-exports.deprecationNotice = deprecationNotice;
+const deprecationNotice = (opts, notice) => {
+  const { cml } = opts;
+  if (cml.driver.warn) {
+    cml.driver.warn(notice);
+  } else {
+    winston.warn(notice);
+  }
+};
+
+exports.addDeprecationNotice = addDeprecationNotice;

src/drivers/github.js

@@ -701,6 +701,10 @@ class Github {
     return command;
   }
 
+  warn(message) {
+    console.log(`::warning::${message}`);
+  }
+
   get sha() {
     if (GITHUB_EVENT_NAME === 'pull_request')
       return github.context.payload.pull_request.head.sha;