Adds failing testcase for .html() result.

**Issue title:** Nested quotes get substituted with ampersand code.
                                            
**Issue description**: when parsing html code with nested quotes, the `.html()` replaces the inner quotes with their ampersend code. Had' just a bit time to dig, so not sure if its an issue of 'htmlparser2' or simply just the excepted behavior. Please correct me if i'm wrong there.
                                            
Created a failing test case, which results:
````
Error: expected
'<label><input id="setbtn" type="button" value="set" ng-click="myVar=&apos;my-class&apos;"></label>'
to equal
'<label><input id="setbtn" type="button" value="set" ng-click="myVar=\'my-class\'"></label>'
````

I know the resulting HTML is legit, still  it should've been modified IMHO.