Update t-SS3 paper (Pattern Recognition Letters)

The paper just got accepted for publication in Elsevier's Pattern Recognition Letters, so I've added a link to the article using the DOI they've provided me.

README.md

@@ -23,8 +23,7 @@ The SS3 text classifier is a novel supervised machine learning model for text cl
 * Well suited for classification over **text streams**.
 * It is not an "obscure" model since it **only has 3 semantically well-defined hyperparameters** which are easy-to-understand.
 
-**Note:** this package also incorporates different variations of the SS3 classifier, such as the one introduced in _"t-SS3: a text classifier with dynamic n-grams for early risk detection over text streams
-"_ (recently submitted to Pattern Recognition Letters, preprint available [here](https://arxiv.org/abs/1911.06147)) which allows SS3 to recognize important word n-grams "on the fly".
+**Note:** this package also incorporates different variations of the SS3 classifier, such as the one introduced in _["t-SS3: a text classifier with dynamic n-grams for early risk detection over text streams"](https://doi.org/10.1016/j.patrec.2020.07.001)_ (preprint available [here](https://arxiv.org/abs/1911.06147)) which allows SS3 to recognize important word n-grams "on the fly".
 
 ## What is PySS3?