Fix Java example mistakenly describes Java environment and runtime as Go

[juwei008]

In the readme file corresponding to the Java example, the Java environment and runtime image are incorrectly described as being for Go. For example: Create a Fission Go environment with the default Go runtime image (this does not include the build environment): fission environment create --name java --image fission/jvm-env --builder fission/jvm-builder

Fixes: #89

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