AOSP/Email - Bump version number to 28 in the XML file.

Bug: 138276176
Bug: 119499886

Test: manual - Ran the following tests on Pixel phone. Tested the email UI.

$ make -j 40
$ make UnifiedEmail -j
$ make Email -j
$ make EmailTests -j

$ ls -l out/target/product/marlin/testcases/Email/arm64/Email.apk out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk
  -rw-r--r-- 1 rtenneti primarygroup 6271433 Aug  5 11:34 out/target/product/marlin/testcases/Email/arm64/Email.apk
  -rw-r--r-- 1 rtenneti primarygroup  389599 Aug  5 11:35 out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk

$ adb install -r -d -g out/target/product/marlin/testcases/Email/arm64/Email.apk
$ adb install -r -d -g out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk
$ adb shell am instrument -w com.android.email.tests
  Time: 2.615
  OK (157 tests)

$ atest EmailTests
  Summary
  -------
  EmailTests: Passed: 157, Failed: 0, Ignored: 0, Assumption Failed: 0

Change-Id: I74bff10c5720a0a9232bae48af25d2bf30c6b6e6
diff --git a/emailcommon/AndroidManifest.xml b/emailcommon/AndroidManifest.xml
index bd1d35d..88573f7 100644
--- a/emailcommon/AndroidManifest.xml
+++ b/emailcommon/AndroidManifest.xml
@@ -2,5 +2,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="com.android.emailcommon"
           android:versionCode="1">
-    <uses-sdk android:targetSdkVersion="24" android:minSdkVersion="14" />
+    <uses-sdk android:targetSdkVersion="28" android:minSdkVersion="14" />
 </manifest>