build on node v4, again (#855)

* build on node v4 + linux, again

* 7 => 8

* 7 => 8 + added 4 back

Author: benmosher

Diff for: .travis.yml

@@ -1,7 +1,8 @@
 language: node_js
 node_js:
+  - 4
   - 6
-  - 7
+  - 8
 
 os:
   - linux

Diff for: appveyor.yml

@@ -1,8 +1,9 @@
 # Test against this version of Node.js
 environment:
   matrix:
-  - nodejs_version: "7"
+  - nodejs_version: "8"
   - nodejs_version: "6"
+  - nodejs_version: "4"
 
 # platform:
 #   - x86