Allow failures on latest Node 7

Because issue othiym23#109 have
not yet been solved for Node.js 7, the test suite currently fails when
running on the latest version of Node.js 7 (v7.10.0 as of this commit).

This commit allows 7.x to fail, but adds an extra build for 7.9.0 which
is know to be good.

This should be reverted when/if Node.js 7 is patched accordingly.

.travis.yml

@@ -6,6 +6,7 @@ cache:
 
 node_js:
   - "7"
+  - "7.9.0"
   - "6"
   - "5"
   - "4"
@@ -17,5 +18,6 @@ matrix:
   allow_failures:
     - node_js: 3
     - node_js: 5
+    - node_js: 7
 
 sudo: false