Update version to 2.2.1 (#45)

Author: rafaelscsilva

README.md

@@ -111,7 +111,6 @@ P. Bota, R. Silva, C. Carreiras, A. Fred, and H. P. da Silva, "BioSPPy: A Python
 
 However, if you want to cite a specific version of BioSPPy, you can use Zenodo's DOI:
 
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 ## License
 BioSPPy is released under the BSD 3-clause license. See LICENSE for more details.