Wrong class name flinkStreamExample instead of streamExample in flink wiki

[PseudoAj]

The instructions to run example flink stream at:

1. https://github.com/InsightDataScience/data-engineering-ecosystem/wiki/flink#running-locally-using-the-command-line
2. https://github.com/InsightDataScience/data-engineering-ecosystem/wiki/flink#running-on-a-cluster

Class name should be streamExample instead of flinkStreamExample.