Use ContextCompat.getColor to support API levels below 23.

Found while debugging on Lollipop.

Change-Id: Ibe97fd30c4ee8cd0c1735a41802b859345f9e931
diff --git a/src/com/android/launcher3/Hotseat.java b/src/com/android/launcher3/Hotseat.java
index c738480..f9424d4 100644
--- a/src/com/android/launcher3/Hotseat.java
+++ b/src/com/android/launcher3/Hotseat.java
@@ -25,6 +25,7 @@
 import android.graphics.Rect;
 import android.graphics.drawable.ColorDrawable;
 import android.graphics.drawable.Drawable;
+import android.support.v4.content.ContextCompat;
 import android.support.v4.graphics.ColorUtils;
 import android.util.AttributeSet;
 import android.view.LayoutInflater;
@@ -69,7 +70,7 @@
         mLauncher = (Launcher) context;
         mHasVerticalHotseat = mLauncher.getDeviceProfile().isVerticalBarLayout();
         mBackgroundColor = ColorUtils.setAlphaComponent(
-                context.getColor(R.color.all_apps_container_color), 0);
+                ContextCompat.getColor(context, R.color.all_apps_container_color), 0);
         mBackground = new ColorDrawable(mBackgroundColor);
         setBackground(mBackground);
     }