DOI of JOSS paper instead of Zenodo [ci skip]

README.md

-limbo [![Build Status](https://travis-ci.org/resibots/limbo.svg?branch=master)](https://travis-ci.org/resibots/limbo) [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.1298561.svg)](https://doi.org/10.5281/zenodo.1298561)
+limbo [![Build Status](https://travis-ci.org/resibots/limbo.svg?branch=master)](https://travis-ci.org/resibots/limbo) [![DOI](http://joss.theoj.org/papers/10.21105/joss.00545/status.svg)](https://doi.org/10.21105/joss.00545)
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 Limbo (LIbrary for Model-Based Optimization) is an open-source C++11 library for Gaussian Processes and data-efficient optimization (e.g., Bayesian optimization) that is designed to be both highly flexible and very fast. It can be used as a state-of-the-art optimization library or to experiment with novel algorithms with "plugin" components.