bpo-13790: Change 'string' to 'specification' in format doc (GH-18690)

(cherry picked from commit 916895f93905f8b8dad677cceff501833f5a633a)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index 89c169a..fa906f7 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -302,9 +302,9 @@
 Most built-in types implement the following options for format specifications,
 although some of the formatting options are only supported by the numeric types.
 
-A general convention is that an empty format string (``""``) produces
+A general convention is that an empty format specification produces
 the same result as if you had called :func:`str` on the value. A
-non-empty format string typically modifies the result.
+non-empty format specification typically modifies the result.
 
 The general form of a *standard format specifier* is: