Decrease targetSdkVersion to 25

Newer targetSdkVersion causes various issues regarding notifications and
background services.

As the AOSP version is not maintained anymore and LineageOS switched to
Etar calendar, let's use this solution.

Issue: FP2A10-196
Change-Id: I171dcd23f1467259298ff213e4b4b435de547470
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 9d3db4a..2b563ef 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -38,7 +38,7 @@
     <uses-permission android:name="android.permission.READ_SYNC_SETTINGS" />
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
     <uses-permission android:name="com.google.android.googleapps.permission.GOOGLE_AUTH.mail" />
-    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="28"></uses-sdk>
+    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="25"></uses-sdk>
 
 
     <application android:name="CalendarApplication"