This should probably be something like...
```lesscss
&:extend(.img-responsive);
```

I know this PR was already rejected; but I still wanted to let you know just to be helpful. :)

In short, extends() will compile as...
```css
.img-responsive,
img[class*="align"],
img[class*="wp-image-"],
img[class*="attachment-"],
.wp-caption { display: block; max-width: 100%; height: auto; }
```

instead of...
```css
.img-responsive { display: block; max-width: 100%; height: auto; }

[...]

img[class*="align"],
img[class*="wp-image-"],
img[class*="attachment-"],
.wp-caption { display: block; max-width: 100%; height: auto; }
```