Fix sass 3.3 mixin extention error
Fix sass 3.3 mixin extention error

Shine18/Timber,swapkats/Materify,tikn/Timber,vovaane/timber,CodeKiwi/dirt,Shopify/Timber,mwcmitchell/Kauai,mwcmitchell/Kauai,kipjib/Timber,gridmechanic/Timber,kipjib/Timber,alexclarkofficial/newbury-theme,montalvomiguelo/Timber,CodeKiwi/dirt,iamdeaneyelid/timber-grunt,CodeKiwi/dirt,swapkats/Materify,iamdeaneyelid/timber-grunt,Shopify/Timber,wad3inthewater/timber-theme,Klaudit/Timber,gridmechanic/Timber,graygilmore/timber-grunt,eugenelardy/shopifytheme,mwcm/Kauai,iamdeaneyelid/timber-grunt,zacwasielewski/Timber,wad3inthewater/timber-theme,triskybro/Timber,alexclarkofficial/newbury-theme,Klaudit/Timber,eugenelardy/shopifytheme,CodeKiwi/dirt,triskybro/Timber,aboutjax/benny,montalvomiguelo/Timber,Shine18/Timber,CodeKiwi/dirt,mwcm/Kauai,mwcm/Kauai,humancopy/Timber,VirtoCommerce/Timber,tikn/Timber,aboutjax/benny,humancopy/Timber,graygilmore/timber-grunt,aboutjax/benny,mwcmitchell/Kauai,vovaane/timber,zacwasielewski/Timber