fix(element-observation): handle extra spacing around css properties

This change allows for any amount of whitespace to be included around css
property names. Previously the style would be lost if there were any extra
whitespace around the property name.

Closes #325

src/element-observation.js

@@ -82,7 +82,7 @@ export class StyleObserver {
         let pairs = newValue.split(/(?:;|:(?!\/))\s*/);
         for( let i = 0, length = pairs.length; i < length; i++ )
         {
-          style = pairs[i];
+          style = pairs[i].trim();
           if ( !style ) { continue; }
 
           styles[style] = version;

test/element-observation.spec.js

@@ -155,7 +155,7 @@ describe('element observation', () => {
       expect(observer instanceof StyleObserver).toBe(true);
       expect(() => observer.subscribe(() => {})).toThrow(new Error('Observation of a "DIV" element\'s "' + attrs[i] + '" property is not supported.'));
 
-      observer.setValue('width: 30px; height:20px; background-color: red;background-image: url("http://aurelia.io/test.png");');
+      observer.setValue(' 	  width : 30px;height:20px; background-color	: red;background-image: url("http://aurelia.io/test.png"); 	 ');
       expect(observer.getValue()).toBe('width: 30px; height: 20px; background-image: url("http://aurelia.io/test.png"); background-color: red;');
       expect(el.style.height).toBe('20px');
       expect(el.style.width).toBe('30px');