Fixes concat operator typo

Author: bryanagee

contributing/code/standards.rst

@@ -96,7 +96,7 @@ Structure
 * Add a single space after each comma delimiter;
 
 * Add a single space around binary operators (``==``, ``&&``, ...), with 
-  the exception of the concatenation (``,``) operator;
+  the exception of the concatenation (``.``) operator;
 
 * Place unary operators (``!``, ``--``, ...) adjacent to the affected variable;