Fix another naming conflict in @+id/content

src/main/res/layout/layout_main.xml

@@ -3,7 +3,7 @@
                 xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools"
                 android:layout_width="match_parent" android:layout_height="match_parent"
                 tools:ignore="UnknownIdInLayout" android:clipChildren="false">
-    <android.support.design.widget.CoordinatorLayout android:id="@+id/content"
+    <FrameLayout android:id="@+id/fragment_holder"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:layout_above="@+id/stat"/>

src/main/scala/com/github/shadowsocks/MainActivity.scala

@@ -146,7 +146,7 @@ class MainActivity extends Activity with ServiceBoundContext with Drawer.OnDrawe
     rxText.setText(TrafficMonitor.formatTraffic(rxTotal))
     txRateText.setText(TrafficMonitor.formatTraffic(txRate) + "/s")
     rxRateText.setText(TrafficMonitor.formatTraffic(rxRate) + "/s")
-    val child = getFragmentManager.findFragmentById(R.id.content).asInstanceOf[ToolbarFragment]
+    val child = getFragmentManager.findFragmentById(R.id.fragment_holder).asInstanceOf[ToolbarFragment]
     if (child != null) child.onTrafficUpdated(txRate, rxRate, txTotal, rxTotal)
   }
 
@@ -337,7 +337,7 @@ class MainActivity extends Activity with ServiceBoundContext with Drawer.OnDrawe
 
   private def displayFragment(fragment: ToolbarFragment) {
     currentFragment = fragment
-    getFragmentManager.beginTransaction().replace(R.id.content, fragment).commitAllowingStateLoss()
+    getFragmentManager.beginTransaction().replace(R.id.fragment_holder, fragment).commitAllowingStateLoss()
     drawer.closeDrawer()
   }