chore: Use node 12 (#141)

chore: Use node 12

Author: germanattanasio

.travis.yml

@@ -29,6 +29,6 @@ deploy:
     repo: watson-developer-cloud/speech-javascript-sdk
 - provider: script
   skip_cleanup: true
-  script: npx semantic-release
+  script: npx semantic-release@15
   on:
-    node: 8
+    node: 12

package.json

@@ -3,6 +3,9 @@
   "version": "0.36.1",
   "description": "IBM Watson Speech to Text and Text to Speech SDK for web browsers.",
   "main": "index.js",
+  "engines": {
+    "node": ">=12"
+  },
   "scripts": {
     "watch-test": "karma start",
     "lint": "eslint .",