travis: use lts/12 nodejs

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

ui/.travis.yml

@@ -1,7 +1,26 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
 language: node_js
 node_js:
-  - 10.15.0
-cache: yarn
+  - 12
+cache:
+  npm: false
+before_install:
+  - npm i -g npm@version-number
 script:
-  - yarn
-  - yarn run lint --no-fix && yarn run build
+  - npm run lint && npm run build