Fix tests on FF.

Author: sorvell

src/HTMLImports.js

@@ -446,9 +446,6 @@ Object.defineProperty(document, '_currentScript', {
   get: function() {
     return HTMLImports.currentScript || document.currentScript;
   },
-  set: function(script) {
-    HTMLImports.currentScript = script;
-  },
   writeable: true,
   configurable: true
 });

test/html/imports/script-1.html

@@ -1,5 +1,5 @@
 <div>me</div>
 <script>
   var d = document._currentScript.ownerDocument.querySelector('div');
-  chai.assert.equal(d.innerText, 'me', '_currentScript can locate element in import')
+  chai.assert.equal(d.innerHTML, 'me', '_currentScript can locate element in import')
 </script>