Update README.md

Author: rikba

README.md

@@ -2,9 +2,9 @@
 This package contains implementations to compute coverage patterns and shortest paths in general polygon with holes.
 Please cite our [accompanying publication](https://arxiv.org/pdf/1907.09224) when using it.
 ```
-Bähnemann, Rik, et al.
-"Revisiting Boustrophedon Coverage Path Planning as a Generalized Traveling Salesman Problem."
-Field and Service Robotics. Springer, Cham, 2019.
+Bähnemann, Rik, et al. 
+"Revisiting boustrophedon coverage path planning as a generalized traveling salesman problem." 
+Field and Service Robotics. Springer, Singapore, 2021.
 ```
 
 ![Coverage Planning in RVIZ](https://user-images.githubusercontent.com/11293852/61134221-70d18980-a4bf-11e9-87a7-d599b60c8dd2.gif)