Update exploring_notebook.md
Update exploring_notebook.md

fix small typo
spark-notebook/spark-notebook,andypetrella/spark-notebook,spark-notebook/spark-notebook,spark-notebook/spark-notebook,maasg/spark-notebook,antonkulaga/spark-notebook,antonkulaga/spark-notebook,antonkulaga/spark-notebook,antonkulaga/spark-notebook,spark-notebook/spark-notebook,andypetrella/spark-notebook,maasg/spark-notebook,andypetrella/spark-notebook,maasg/spark-notebook,andypetrella/spark-notebook,maasg/spark-notebook