Add dot at the end of the docstring following pep257

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

pydocstringformatter/formatting/base.py

@@ -3,19 +3,19 @@
 
 
 class Formatter:
-    """Base class for docstring formatter"""
+    """Base class for docstring formatter."""
 
     @abc.abstractmethod
     def treat_token(self, tokeninfo: tokenize.TokenInfo) -> tokenize.TokenInfo:
-        """Return a modified token"""
+        """Return a modified token."""
 
 
 class StringFormatter(Formatter):
-    """Base class for formatter that only modifies the string content"""
+    """Base class for formatter that only modifies the string content."""
 
     @abc.abstractmethod
     def _treat_string(self, tokeninfo: tokenize.TokenInfo) -> str:
-        """Return a modified string"""
+        """Return a modified string."""
 
     def treat_token(self, tokeninfo: tokenize.TokenInfo) -> tokenize.TokenInfo:
         return tokenize.TokenInfo(