Support for gradle 9.0.0

[ricardoboss]

With version 0.6.0 and this in gradle-wrapper.properties:

distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-all.zip

everything builds fine.

Then I update it to:

distributionUrl=https\://services.gradle.org/distributions/gradle-9.0.0-all.zip

the build fails with:

Running Gradle task 'bundleRelease'...                          

FAILURE: Build completed with 2 failures.

1: Task failed with an exception.
-----------
* Where:
Build file '/Users/ricardo/.pub-cache/hosted/pub.dev/flutter_libserialport-0.6.0/android/build.gradle' line: 8

* What went wrong:
A problem occurred evaluating project ':flutter_libserialport'.
> Could not find method jcenter() for arguments [] on repository container of type org.gradle.api.internal.artifacts.dsl.DefaultRepositoryHandler.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to generate a Build Scan (Powered by Develocity).
> Get more help at https://help.gradle.org.
==============================================================================

2: Task failed with an exception.
-----------
* What went wrong:
A problem occurred configuring project ':flutter_libserialport'.
> Failed to notify project evaluation listener.
   > java.lang.NullPointerException (no error message)
   > java.lang.NullPointerException (no error message)

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to generate a Build Scan (Powered by Develocity).
> Get more help at https://help.gradle.org.
==============================================================================

BUILD FAILED in 8s
Running Gradle task 'bundleRelease'...                              8.8s
Gradle task bundleRelease failed with exit code 1
Failed to run flutter build.

The second failure is probably caused by the first one.