docs: update recommended NDK -> r25b (LTS)

ref:

- https://developer.android.com/ndk/downloads
- https://github.com/android/ndk/wiki/Changelog-r25

Author: Christopher J. Brody

README.md

@@ -137,7 +137,7 @@ For applications which utilize ProGuard, a few additional rules must be included
 
 ### Building
 
-In order to build `android-database-sqlcipher` from source you will need both the Android SDK, Gradle, Android NDK, SQLCipher core source directory, and an OpenSSL source directory. We currently recommend using Android NDK LTS version `23.0.7599858`.
+In order to build `android-database-sqlcipher` from source you will need both the Android SDK, Gradle, Android NDK, SQLCipher core source directory, and an OpenSSL source directory. We currently recommend using Android NDK LTS version `25.1.8937393` (r25b).
 
 To complete the `make` command, the `ANDROID_NDK_HOME` environment variable must be defined which should point to your NDK root. Once you have cloned the repo, change directory into the root of the repository and run the following commands: