upgrade xiaomi push to 5.9.9 (#240)

Author: jwfing

android-sdk/mixpush-xiaomi/build.gradle

@@ -5,7 +5,7 @@ android {
     buildToolsVersion "28.0.3"
 
     defaultConfig {
-        minSdkVersion 17
+        minSdkVersion 19
         targetSdkVersion 26
         versionCode 1
         versionName "1.0"
@@ -60,7 +60,7 @@ android.libraryVariants.all { variant ->
 }
 
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
+    implementation fileTree(dir: 'libs', include: ['*.aar'])
 
     implementation project(':realtime-android')
     implementation project(':storage-android')