feat(docs): add markdown linter for exercises README.md files

exercises/hashmaps/README.md

@@ -1,6 +1,7 @@
 # Hashmaps
+
 A *hash map* allows you to associate a value with a particular key.
-You may also know this by the names [*unordered map* in C++](https://en.cppreference.com/w/cpp/container/unordered_map), 
+You may also know this by the names [*unordered map* in C++](https://en.cppreference.com/w/cpp/container/unordered_map),
 [*dictionary* in Python](https://docs.python.org/3/tutorial/datastructures.html#dictionaries) or an *associative array* in other languages.
 
 This is the other data structure that we've been talking about before, when