fix(no-unused-css): blank lines being left after fixing

[rafaelss95]

Currently, when you use no-unused-css's autofix, it only replaces the unused classes with an empty string, which results in many blank lines. Sample:

Input:

.test {
  color: #fff;
}
div{color: #fff;}
.test-2 {
  color: #fff;
}
.test-3 {color: #fff}
.test-4{                color:#fff;font-size: 12px;







}

button {
  color: #fff;
}

Current output:

- .test {
-   color: #fff;
- }
- div{color: #fff;}
- .test-2 {
-   color: #fff;
- }
- .test-3 {color: #fff}
- .test-4{                color:#fff;font-size: 12px;
- 
- 
- 

+ div{color: #fff;}



- }

button {
  color: #fff;
}

Output using these changes:

- .test {
-   color: #fff;
- }
- div{color: #fff;}
- .test-2 {
-   color: #fff;
- }
- .test-3 {color: #fff}
- .test-4{                color:#fff;font-size: 12px;
- 
- 
- 
- 
- 
-  
- }
+ div{color: #fff;}

button {
  color: #fff;
}