CodingGuidelines: write punctuation marks

- Match style in Release Notes

Signed-off-by: Josh Soref <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jsoref

Documentation/CodingGuidelines

@@ -578,7 +578,7 @@ Externally Visible Names
    . The variable name describes the effect of tweaking this knob.
 
    The section and variable names that consist of multiple words are
-   formed by concatenating the words without punctuations (e.g. `-`),
+   formed by concatenating the words without punctuation marks (e.g. `-`),
    and are broken using bumpyCaps in documentation as a hint to the
    reader.