Incorrect documentation for BigDecimal#sign

[carl-stripe]

The documentation for BigDecimal#sign is incorrect. It reads:

Returns a positive value if > 0, a negative value if < 0, and a zero if == 0.

bigdecimal/ext/bigdecimal/bigdecimal.c

Lines 2735 to 2736 in f3e6bfd

	* Returns a positive value if > 0, a negative value if < 0, and a
	* zero if == 0.

However, this does not match BigDecimal's behavior:

[1] pry(main)> require 'bigdecimal'
=> true
[2] pry(main)> BigDecimal.new("0").sign
=> 1
[3] pry(main)> BigDecimal.new("-0").sign
=> -1

These values match the BigDecimal::SIGN_XXX constants for signed zeroes, which have the values 1 and -1 (neither of which is zero as #sign seems to document)