Fix regex for the json-file logger opts in overview.md
The regex used to describe the max-file and max-size logging options for
the json-file logger were incorrect. The regexes would only match a
single character (a digit or a literal +). Instead the regexes should
match 1 or more digits.
The character class for the units of the max-size also included a pipe
which meant that the regex would match 1| instead of only matching 1m,
1k, and 1g.
Signed-off-by: Steven Erenst <stevenerenst@gmail.com>