[test] Remove IE6 and IE7 tests (#581)

Related: https://wiki.saucelabs.com/pages/viewpage.action?pageId=70068108

Author: darrachequesne

.travis.yml

@@ -3,7 +3,7 @@ sudo: false
 node_js:
   - '4'
   - '6'
-  - '7'
+  - '8'
 git:
   depth: 1
 notifications:
@@ -16,10 +16,6 @@ matrix:
     env: BROWSER_NAME=safari BROWSER_VERSION=latest
   - node_js: 'node'
     env: BROWSER_NAME=firefox BROWSER_VERSION=latest
-  - node_js: 'node'
-    env: BROWSER_NAME=ie BROWSER_VERSION=6
-  - node_js: 'node'
-    env: BROWSER_NAME=ie BROWSER_VERSION=7
   - node_js: 'node'
     env: BROWSER_NAME=ie BROWSER_VERSION=8
   - node_js: 'node'