bpo-32720: Fixed the definition for width and precision in format mini-language doc (GH-5482)

Changed the definition of width and precision from "integer" to "digit+" in format mini-language doc.

Doc/library/string.rst

@@ -304,9 +304,9 @@ The general form of a *standard format specifier* is:
    fill: <any character>
    align: "<" | ">" | "=" | "^"
    sign: "+" | "-" | " "
-   width: `integer`
+   width: `digit`+
    grouping_option: "_" | ","
-   precision: `integer`
+   precision: `digit`+
    type: "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
 
 If a valid *align* value is specified, it can be preceded by a *fill*