fix a small typo that attachShadow needs an argument

Author: gdh1995

content_scripts/ui_component.coffee

@@ -27,7 +27,8 @@ class UIComponent
         seamless: "seamless"
       shadowWrapper = DomUtils.createElement "div"
       # PhantomJS doesn't support createShadowRoot, so guard against its non-existance.
-      @shadowDOM = shadowWrapper.attachShadow?() ? shadowWrapper.createShadowRoot?() ? shadowWrapper
+      @shadowDOM = shadowWrapper.attachShadow?( mode: "open" ) ?
+        shadowWrapper.createShadowRoot?() ? shadowWrapper
       @shadowDOM.appendChild styleSheet
       @shadowDOM.appendChild @iframeElement
       @toggleIframeElementClasses "vimiumUIComponentVisible", "vimiumUIComponentHidden"

content_scripts/vimium_frontend.coffee

@@ -247,7 +247,7 @@ flashFrame = do ->
       # PhantomJS doesn't support createShadowRoot, so guard against its non-existance.
       # https://hacks.mozilla.org/2018/10/firefox-63-tricks-and-treats/ says
       # Firefox 63 has enabled Shadow DOM v1 by default
-      _shadowDOM = highlightedFrameElement.attachShadow?() ?
+      _shadowDOM = highlightedFrameElement.attachShadow?( mode: "open" ) ?
         highlightedFrameElement.createShadowRoot?() ? highlightedFrameElement
 
       # Inject stylesheet.