zuul: drop IE6-7 tests

IE6 and IE7 tests stopped working at some point, presumably because
some dependency of zuul or browserify added a dangling comma or some
feature that these browsers don't support.

I don't have the time/patience to debug this now. buffer probably works
in IE6-7 still, but I'm dropping the tests for it. If someone wants to
fix the issue and re-enable these tests, you're welcome to :)

.zuul.yml

@@ -9,7 +9,7 @@ browsers:
   - name: safari
     version: 5..latest
   - name: ie
-    version: 6..latest
+    version: 8..latest
   - name: opera
     version: 11..latest
   - name: iphone

bin/download-node-tests.js

@@ -56,7 +56,9 @@ function testfixer (filename) {
 
     if (firstline) {
       // require buffer explicitly
-      line = 'var Buffer = require(\'../../\').Buffer\nif (process.env.OBJECT_IMPL) Buffer.TYPED_ARRAY_SUPPORT = false\n' + line
+      line = 'var Buffer = require(\'../../\').Buffer\n' +
+        'if (process.env.OBJECT_IMPL) Buffer.TYPED_ARRAY_SUPPORT = false\n' +
+        line
       firstline = false
     }