Fix Issue 59989

Case typo in documentation for <application> tag

Signed-off-by: Paul Quei <paulquei@gmail.com>

On the page http://developer.android.com/guide/topics/manifest/application-element.html,
in the "ATTRIBUTES" section,
the heading "android:allowbackup" should be
"android:allowBackup" (ie. upper case "B").

Change-Id: I7cab16729ea2ffc653bc449009ff983a05f6e867