Fix `license` metadata

We recently updated the datasets metadata for consistency with other repo types (models & spaces)

Thanks! 🙏

README.md

@@ -1,7 +1,7 @@
 ---
-languages:
+language:
 - si
-licenses:
+license:
 - mit
 ---
 This repo contains data and source code for the paper Nanayakkara, P., & Ranathunga, S. (2018, May). Clustering Sinhala News Articles Using Corpus-Based Similarity Measures. In 2018 Moratuwa Engineering Research Conference (MERCon) (pp. 437-442). IEEE.