https://github.com/tracim/tracim/issues/798, fix design of admin button on the header

frontend/src/css/Header.styl

       list-style none
       &__adminlink
         .adminlink
-          border 1px solid grey
-          border-radius 5px
           &__btn
+            margin-right 15px
+            border 1px solid grey
+            border-radius 5px
+            background-color transparent
             &::after
               margin-left 15px
           &__setting
           margin-right 30px
           .btnquestion__icon
             color darkGrey
-      &__adminlink
-        margin-right 15px
-        .adminlink__btn
-          border none
-          cursor pointer
-          background-color transparent
       &__itemprofil
         .profilgroup
           margin-right 30px