Fix appengine-java8 README Hello World section

[redwrasse]

In which file did you encounter the issue?

README in appengine-java8

https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/appengine-java8

Did you change the file? If so, how?

Describe the issue

Hello World links in README are incorrect/missing

[kurtisvg]

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