[Tests] pin included builds to LTS instead of “latest”, since node 9 is...

[Tests] pin included builds to LTS instead of “latest”, since node 9 is broken; use `nvm install-latest-npm` so new npm doesn’t break older node

.travis.yml

 language: node_js
 node_js:
+  - "9"
   - "8"
   - "7"
   - "6"
   - "4"
   - "iojs"
+before_install:
+  - 'nvm install-latest-npm'
 before_script:
   - 'if [ -n "${KARMA-}" ]; then export DISPLAY=:99.0; fi'
   - 'if [ -n "${KARMA-}" ]; then sh -e /etc/init.d/xvfb start; fi'
@@ -25,13 +28,14 @@ sudo: false
 matrix:
   fast_finish: true
   include:
-    - node_js: "node"
+    - node_js: "lts/*"
       env: COVERAGE=true TEST=false
-    - node_js: "node"
+    - node_js: "lts/*"
       env: KARMA=true TEST=false
-    - node_js: "node"
+    - node_js: "lts/*"
       env: LINT=true TEST=false
   allow_failures:
+    - node_js: "9"
     - node_js: "7"
     - node_js: "iojs"
     - env: KARMA=true TEST=false