Use hex value instead of rgba for gray border color

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/framework/variables.scss

@@ -121,7 +121,7 @@ $border-white-normal: #d6dae2;
 $border-white-dark: #c6cacf;
 
 $border-gray-light: #dcdcdc;
-$border-gray-normal: rgba(0, 0, 0, 0.10);
+$border-gray-normal: #d7d7d7;
 $border-gray-dark: #c6cacf;
 
 $border-green-light: #2faa60;