Fix a "reproduce me" button (#68)

Author: Arpit-Babbar

index.md

@@ -169,7 +169,7 @@ listed above. Author names of Trixi.jl's main developers are in *italics*.
   **An Entropy-Stable Discontinuous Galerkin Discretization of the Ideal Multi-Ion Magnetohydrodynamics System**, 2024.\\
   [![arXiv:2402.14615](https://img.shields.io/badge/arXiv-2402.14615-yellow)](https://arxiv.org/abs/2402.14615)
   [![doi:10.1016/j.jcp.2024.113655](https://zenodo.org/badge/doi/10.1016/j.jcp.2024.113655.svg)](https://doi.org/10.1016/j.jcp.2024.113655)
-  [![reproduce me!](https://github.com/amrueda/paper_2024_multi-ion_mhd)
+  [![reproduce me!](https://img.shields.io/badge/reproduce-me!-brightgreen)](https://github.com/amrueda/paper_2024_multi-ion_mhd)
 
 * *Doehring*, *Gassner*, Torrilhon,
   **Many-Stage Optimal Stabilized Runge-Kutta Methods for Hyperbolic Partial Differential Equations**, 2024.\\