minor correction to tutorial 2.1
minor correction to tutorial 2.1

Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine,Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine,Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine,Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine,Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine,Zhong-Lab-UCSD/Genomic-Interactive-Visualization-Engine