[Tests] up to node v9.3, v8.8, v6.12; pin included builds to LTS

Author: ljharb

.travis.yml

@@ -2,9 +2,10 @@ language: node_js
 os:
  - linux
 node_js:
-  - "8.8"
+  - "9.3"
+  - "8.9"
   - "7.10"
-  - "6.11"
+  - "6.12"
   - "5.12"
   - "4.8"
   - "iojs-v3.3"
@@ -29,8 +30,16 @@ env:
 matrix:
   fast_finish: true
   include:
-    - node_js: "node"
+    - node_js: "lts/*"
       env: PRETEST=true
+    - node_js: "9.2"
+      env: TEST=true ALLOW_FAILURE=true
+    - node_js: "9.1"
+      env: TEST=true ALLOW_FAILURE=true
+    - node_js: "9.0"
+      env: TEST=true ALLOW_FAILURE=true
+    - node_js: "8.8"
+      env: TEST=true ALLOW_FAILURE=true
     - node_js: "8.7"
       env: TEST=true ALLOW_FAILURE=true
     - node_js: "8.6"
@@ -67,6 +76,8 @@ matrix:
       env: TEST=true ALLOW_FAILURE=true
     - node_js: "7.0"
       env: TEST=true ALLOW_FAILURE=true
+    - node_js: "6.11"
+      env: TEST=true ALLOW_FAILURE=true
     - node_js: "6.10"
       env: TEST=true ALLOW_FAILURE=true
     - node_js: "6.9"