Fix typos in comments.

Author: cscott

src/css/Parser.js

@@ -2134,7 +2134,7 @@ Parser.prototype = function(){
                  * or
                  * S* '{' S* [ declaration | margin ]? [ ';' S* [ declaration | margin ]? ]* '}' S*
                  * Note that this is how it is described in CSS3 Paged Media, but is actually incorrect.
-                 * A semicolon is only necessary following a declaration is there's another declaration
+                 * A semicolon is only necessary following a declaration if there's another declaration
                  * or margin afterwards.
                  */
                 var tokenStream = this._tokenStream,

src/css/PropertyValueIterator.js

@@ -105,7 +105,7 @@ PropertyValueIterator.prototype.next = function(){
  * Returns the previous part of the property value or null if there is no
  * previous part.
  * @return {parserlib.css.PropertyValuePart} The previous part of the
- * property value or null if there is no next part.
+ * property value or null if there is no previous part.
  * @method previous
  */
 PropertyValueIterator.prototype.previous = function(){