ci: remove stale config for node 4 and below (#17012)

.travis.yml

@@ -1,20 +1,10 @@
 language: node_js
 
 node_js:
-  - '8'
+  - 'lts/*'
 
 cache:
   directories:
     - node_modules
 
-env:
-  - CXX=g++-4.8
-
-addons:
-  apt:
-    sources:
-      - ubuntu-toolchain-r-test
-    packages:
-      - g++-4.8
-
 sudo: false