Fix repeated word in part13a.md

Author: diegosouzajp

src/content/13/en/part13a.md

@@ -63,7 +63,7 @@ There are both advantages and disadvantages to not having a schema. One of the a
 
 The relational databases that are the focus of this section, on the other hand, lean heavily on the existence of a schema, and the advantages and disadvantages of schema databases are almost the opposite compared of the non-schema databases.
 
-The reason why the the previous sections of the course used MongoDB is precisely because of its schema-less nature, which has made it easier to use the database for someone with little knowledge of relational databases. For most of the use cases of this course, I personally would have chosen to use a relational database.
+The reason why the previous sections of the course used MongoDB is precisely because of its schema-less nature, which has made it easier to use the database for someone with little knowledge of relational databases. For most of the use cases of this course, I personally would have chosen to use a relational database.
 
 ### Application database