fix: border-radius for hint button

Author: sota1235

browser/main/modals/PreferencesModal/ConfigTab.styl

@@ -64,6 +64,7 @@
 .group-control-leftButton
   colorDefaultButton()
   border none
+  border-radius 5px
   font-size $tab--button-font-size
   height $tab--button-height
   padding 0 15px