Update tested version matrix

Based on current node.js published support table:
https://github.com/nodejs/Release#release-schedule

Continue to support 0.10.x, 0.12.x, and 4.x legacy stable branches. 9.x
has been deprecated so include its stable successor of v10.x instead.

.travis.yml

@@ -1,15 +1,11 @@
 language: node_js
 node_js:
 - stable
-- "9.0"
-- "8.0"
-- "7.0"
-- "6.0"
-- "5.12"
-- "5.0"
-- "4.4"
-- "4.0"
-- "0.12"
-- "0.10"
+- "v10.*"
+- "v8.*"
+- "v6.*"
+- "v4.*"
+- "v0.12.*"
+- "v0.10.*"
 matrix:
   fast_finish: true