fix #60 - writable for polyfilled properties

src/index.js

@@ -749,6 +749,10 @@ if (!('attachShadow' in document.createElement('div'))) {
 
     // All properties should be configurable.
     memberProperty.configurable = true;
+    // Applying to the data properties only since we can't have writable accessor properties
+    if (memberProperty.hasOwnProperty('value')) {
+      memberProperty.writable = true
+    }
 
     // Polyfill as much as we can and work around WebKit in other areas.
     if (canPatchNativeAccessors || polyfillAtRuntime.indexOf(memberName) === -1) {

test/unit/shadow/polyfill.js

@@ -53,6 +53,13 @@ describe('shadow/polyfill', function () {
     });
   }
 
+  it('polyfilled properties with value should be writable', function() {
+    let elem = create('div');
+
+    expect(elem.removeEventListener).not.to.equal("");
+    elem.removeEventListener = "";
+    expect(elem.removeEventListener).to.equal("");
+  });
 
   describe('api', function () {
     let host, root;