Update README.md

Added DOI badges to both publications.

README.md

@@ -4,9 +4,9 @@
 [![Latest version](https://img.shields.io/badge/Latest_version-2.1-brightgreen.svg?style=plastic)](https://github.com/draeger-lab/SBSCL/releases/)
 [![DOI](https://img.shields.io/badge/DOI-10.20944%2Fpreprints202012.0296.v1-blue.svg?style=plastic)](https://doi.org/10.20944/preprints202012.0296.v1)
 [![Maven Central](https://img.shields.io/maven-central/v/org.draegerlab/sbscl.svg?style=plastic&label=Maven%20Central)](https://search.maven.org/search?q=g:%22org.draegerlab%22%20AND%20a:%22sbscl%22)
+[![Build Status](https://img.shields.io/travis/com/draeger-lab/SBSCL.svg?style=plastic)](https://travis-ci.com/draeger-lab/SBSCL)
 ![Code Size](https://img.shields.io/github/languages/code-size/draeger-lab/SBSCL.svg?style=plastic)
 ![Downloads of all releases](https://img.shields.io/github/downloads/draeger-lab/SBSCL/total.svg?style=plastic)
-[![Build Status](https://img.shields.io/travis/com/draeger-lab/SBSCL.svg?style=plastic)](https://travis-ci.com/draeger-lab/SBSCL)
 
 *Authors*: [Roland Keller](https://github.com/RolandKeller5), [Andreas Dräger](https://github.com/draeger), [Hemil Panchiwala](https://github.com/hemilpanchiwala), [Shalin Shah](https://github.com/shalinshah1993), [Matthias König](https://github.com/matthiaskoenig), [Alexander Dörr](https://github.com/a-doerr), [Richard Adams](https://github.com/otter606)
 
@@ -16,8 +16,10 @@
 
 When using SBSCL in a research work, please cite the following works:
 
-1. Panchiwala, H.; Shah, S.; Planatscher, H.; Zakharchuk, M.; König, M.; Dräger, A. The Systems Biology Simulation Core Library. Preprints 2020, 2020120296. [doi: 10.20944/preprints202012.0296.v1](https://doi.org/10.20944/preprints202012.0296.v1).
-2. Keller, R.; Dörr, A.; Tabira, A.; Funahashi, A.; Ziller, M.J.; Adams, R.; Rodriguez, N.; Le Novère, N.; Hiroi, N.; Planatscher, H.; Zell A.; Dräger; A. The systems biology simulation core algorithm. BMC Syst Biol 7, 55 (2013). [doi: 10.1186/1752-0509-7-55](https://doi.org/10.1186/1752-0509-7-55).
+1. Panchiwala, H.; Shah, S.; Planatscher, H.; Zakharchuk, M.; König, M.; Dräger, A. The Systems Biology Simulation Core Library. Preprints 2020, 2020120296.
+   [![DOI](https://img.shields.io/badge/DOI-10.20944%2Fpreprints202012.0296.v1-blue.svg?style=plastic)](https://doi.org/10.20944/preprints202012.0296.v1)
+2. Keller, R.; Dörr, A.; Tabira, A.; Funahashi, A.; Ziller, M.J.; Adams, R.; Rodriguez, N.; Le Novère, N.; Hiroi, N.; Planatscher, H.; Zell A.; Dräger; A. The systems biology simulation core algorithm. BMC Syst Biol 7, 55 (2013).
+   [![DOI](https://img.shields.io/badge/DOI-10.1186%2F1752--0509--7--55-blue.svg?style=plastic)](https://doi.org/10.1186/1752-0509-7-55)
 
 ### Description
 The Systems Biology Simulation Core Library (SBSCL) provides an efficient and exhaustive Java™ implementation of methods to interpret the content of models encoded in the Systems Biology Markup Language ([SBML](http://sbml.org)) and its numerical solution. This library is based on the [JSBML](http://sbml.org/Software/JSBML) project. It can be used on every operating system for which a Java Virtual Machine is available. Please note that this project does not contain any user interface neither a command-line interface, nor a graphical user interface. This project has been developed as a pure programming library. To support the [MIASE](http://co.mbine.org/standards/miase) effort, it understands [SED-ML](http://sed-ml.org) files. Its abstract type and interface hierarchy facilitates the implementation of further community standards, such as [CellML](https://www.cellml.org).