chore: Remove deprecated jcenter repo (aws-amplify#9397)

#### Description of changes

Just trying to eliminate warnings about this repo being deprecated.
https://developer.android.com/studio/build/jcenter-migration

#### Description of how you validated changes

Brought this new version of build.gradle into my own project's
node_modules/amazon-cognito-identity-js folder and checked that it still
builds correctly.

#### Checklist

- [x] PR description included
- [x] `yarn test` passes

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

packages/amazon-cognito-identity-js/android/build.gradle

@@ -1,6 +1,6 @@
 buildscript {
     repositories {
-        jcenter()
+        mavenCentral()
     }
 
     dependencies {