Fix links

dtsms/dtsms.md

 # A Systematic Cross-Domain Mapping Study on the Software Engineering of Digital Twins
 
 For better transparency and replicability, this directory provides
-* a list of the [initial 2002 publications](dtsms/2021-DTSMS-InitialSearch.xlsx) and
-* a list of the [356 included publication](dtsms/20201-DTSMS-Included.xlsx).
+* a list of the [initial 2002 publications](2021-DTSMS-InitialSearch.xlsx) and
+* a list of the [356 included publication](20201-DTSMS-Included.xlsx).