Fix precision_with_grouping in formatting mini-language

The 'type' field can't immediately follow to the dot.
This amends f39a07b.

Author: skirpichev

Doc/library/string.rst

@@ -326,7 +326,7 @@ The general form of a *standard format specifier* is:
    sign: "+" | "-" | " "
    width_and_precision: [`width_with_grouping`][`precision_with_grouping`]
    width_with_grouping: [`width`][`grouping`]
-   precision_with_grouping: "." [`precision`][`grouping`]
+   precision_with_grouping: "." (`precision` [`grouping`] | `grouping`)
    width: `~python-grammar:digit`+
    precision: `~python-grammar:digit`+
    grouping: "," | "_"