update build.gradle to stop using old API

[imanushin]

I found three usages of old Gradle API:

• maven plugin is deprecated
• jcenter is deprecated
• compile/testCompile are deprecated

No any gradle-related issues are exists for now (checked locally with --warning-mode all option):

19:28:29: Executing 'build --warning-mode all'...

Starting Gradle Daemon...
Gradle Daemon started in 1 s 200 ms

> Task :compileJava
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :processResources UP-TO-DATE
> Task :classes
> Task :jar
> Task :publishPluginJar UP-TO-DATE
> Task :javadoc
> Task :publishPluginJavaDocsJar
> Task :assemble

> Task :compileTestJava

> Task :processTestResources UP-TO-DATE
> Task :testClasses
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: C:\git\markdown-confluence-gradle-plugin\src\test\java\com\github\qwazer\markdown\confluence\core\service\ConfluenceServiceTestWithMocks.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
> Task :test
> Task :check
> Task :build

BUILD SUCCESSFUL in 16s
9 actionable tasks: 6 executed, 3 up-to-date
19:28:48: Execution finished 'build --warning-mode all'.

[imanushin]

Links:

• https://discuss.gradle.org/t/plugin-with-id-maven-not-found/39621
• https://stackoverflow.com/questions/23796404/could-not-find-method-compile-for-arguments-gradle
• https://blog.gradle.org/jcenter-shutdown