column, range-diff: downcase option description

column, range-diff: downcase option description

It is customary not to begin the help text for each option given to
the parse-options API with a capital letter. Various (sub)commands'
option arrays don't follow the guideline provided by the parse_options
Documentation regarding the descriptions.

Downcase the first word of some option descriptions for "column"
and "range-diff".

Signed-off-by: Chinmoy Chakraborty <chinmoy12c@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>