使用 Gradle 导入的方式集成 SDK 后，消息推送时崩溃

按照官网的教程，导入 ChatKit 后，在测试时发现收到消息推送时会崩溃，从 log 看是和 Notification 生成相关的地方出了问题。但是采用源代码导入的方式导入时没有这个问题。

相关 log

java.lang.NoClassDefFoundError: Failed resolution of: Lcom/avos/avospush/notification/NotificationCompat$Builder;
                                                       at cn.leancloud.chatkit.utils.LCIMNotificationUtils.showNotification(LCIMNotificationUtils.java:68)
                                                       at cn.leancloud.chatkit.handler.LCIMMessageHandler$1.internalDone0(LCIMMessageHandler.java:96)
                                                       at cn.leancloud.chatkit.handler.LCIMMessageHandler$1.internalDone0(LCIMMessageHandler.java:88)
                                                       at com.avos.avoscloud.AVCallback.internalDone(AVCallback.java:18)
                                                       at cn.leancloud.chatkit.cache.LCIMProfileCache$1.internalDone0(LCIMProfileCache.java:76)
                                                       at cn.leancloud.chatkit.cache.LCIMProfileCache$1.internalDone0(LCIMProfileCache.java:71)
                                                       at com.avos.avoscloud.AVCallback.internalDone(AVCallback.java:18)
                                                       at cn.leancloud.chatkit.cache.LCIMProfileCache.getCachedUsers(LCIMProfileCache.java:105)
                                                       at cn.leancloud.chatkit.cache.LCIMProfileCache.getCachedUser(LCIMProfileCache.java:71)
                                                       at cn.leancloud.chatkit.handler.LCIMMessageHandler.sendNotification(LCIMMessageHandler.java:88)
                                                       at cn.leancloud.chatkit.handler.LCIMMessageHandler.onMessage(LCIMMessageHandler.java:55)
                                                       at cn.leancloud.chatkit.handler.LCIMMessageHandler.onMessage(LCIMMessageHandler.java:31)
                                                       at com.avos.avoscloud.im.v2.MessageHandler.processMessage(MessageHandler.java:33)
                                                       at com.avos.avoscloud.im.v2.MessageHandler.processEvent0(MessageHandler.java:26)
                                                       at com.avos.avoscloud.AVIMEventHandler$1.run(AVIMEventHandler.java:13)
                                                       at android.os.Handler.handleCallback(Handler.java:751)
                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                       at android.os.Looper.loop(Looper.java:154)
                                                       at android.app.ActivityThread.main(ActivityThread.java:6126)
                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                    Caused by: java.lang.ClassNotFoundException: Didn't find class "com.avos.avospush.notification.NotificationCompat$Builder"
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
09-08 16:39:45.042 28708-28708/? E/AndroidRuntime:     at java.lang.ClassLoader.loadClass(ClassLoader.java:380)
                                                       at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
                                                           ... 22 more

leancloud / LeanCloudChatKit-Android

使用 Gradle 导入的方式集成 SDK 后，消息推送时崩溃 #63