add [openjdk11] to Travis build

[sullis]

Fixes

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the development branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

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[thinkingserious]

Hello @sullis,

It looks like there are some errors that need resolving before we can merge this one in.

With best regards,

Elmer

[sullis]

This project uses an outdated version of Gradle.

Exception is:
java.lang.IllegalArgumentException: Could not determine java version from '11.0.2'.
	at org.gradle.api.JavaVersion.toVersion(JavaVersion.java:65)
	at org.gradle.api.JavaVersion.current(JavaVersion.java:74)
	at org.gradle.internal.jvm.Jvm.<init>(Jvm.java:84)
	at org.gradle.internal.jvm.Jvm.create(Jvm.java:63)
	at org.gradle.internal.jvm.Jvm.current(Jvm.java:49)
	at org.gradle.launcher.daemon.configuration.CurrentProcess.<init>(CurrentProcess.java:32)
	at org.gradle.launcher.cli.BuildActionsFactory.canUseCurrentProcess(BuildActionsFactory.java:149)
	at org.gradle.launcher.cli.BuildActionsFactory.createAction(BuildActionsFactory.java:129)
	at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.createAction(CommandLineActionFactory.java:206)
	at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:196)
	at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:174)
	at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:170)
	at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:139)
	at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:33)
	at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:22)
	at org.gradle.launcher.Main.doAction(Main.java:46)
	at org.gradle.launcher.bootstrap.EntryPoint.run(EntryPoint.java:45)

[childish-sambino]

Added as part of #599