fix: removed formatting error in slides of lecture 13

lectures/revealjs/13-lecture-commit.adoc

@@ -189,6 +189,7 @@ https://xkcd.com/1296/
 - add information about testing, especially if there are manual tests needed  
 
 == What to write in the commit message (2)
+
 Finally, read the message before committing as it might reveal that you should split it in smaller commits
 
 == Enforcing commit message format