chore: fix IE issues

Author: crisbeto

src/lib/icon/icon-registry.ts

@@ -378,8 +378,8 @@ export class MdIconRegistry {
   private _toSvgElement(element: Element): SVGElement {
     let svg = this._svgElementFromString('<svg></svg>');
 
-    for (let i = 0; i < element.children.length; i++) {
-      svg.appendChild(element.children[i].cloneNode(true));
+    for (let i = 0; i < element.childNodes.length; i++) {
+      svg.appendChild(element.childNodes[i].cloneNode(true));
     }
 
     return svg;

src/lib/icon/icon.spec.ts

@@ -254,12 +254,11 @@ describe('MdIcon', () => {
       fixture.detectChanges();
 
       const svgElement = verifyAndGetSingleSvgChild(mdIconElement);
-      const firstChild = svgElement.children[0];
+      const path = svgElement.querySelector('path');
 
       expect(svgElement.querySelector('symbol')).toBeFalsy();
-      expect(svgElement.children.length).toBe(1);
-      expect(firstChild.nodeName.toLowerCase()).toBe('path');
-      expect(firstChild.getAttribute('id')).toBe('quack');
+      expect(path).toBeTruthy();
+      expect(path.getAttribute('id')).toBe('quack');
     });
 
     it('should not wrap <svg> elements in icon sets in another svg tag', () => {