[site:test] Fix browser tests again

expect.js doesn't play nicely with Babel, so it
shouldn't be transformed by Babelify.^1 Note that
the ignore option in Babelify is buggy ^2, so
this might not work on your end.

^1 Automattic/expect.js#149
^2 babel/babelify#265

tools/build-test.js

@@ -6,6 +6,9 @@ var babelify = require('babelify')
 browserify()
   .exclude(['citation-js'])
   .add('./test/wrapper.js')
-  .transform(babelify, {global: true})
+  .transform(babelify, {
+    global: true,
+    ignore: ['node_modules/expect.js/']
+  })
   .bundle()
   .pipe(fs.createWriteStream(path.join(__dirname, '../build/test.citation.js')))