adds animation to color on outlined btns

Author: andresgalante

scss/_variables.scss

@@ -343,7 +343,7 @@ $btn-border-radius:           $border-radius !default;
 $btn-border-radius-lg:        $border-radius-lg !default;
 $btn-border-radius-sm:        $border-radius-sm !default;
 
-$btn-transition:              background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;
+$btn-transition:              background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out, color .15s ease-in-out !default;
 
 
 // Forms