darker background for face `show-paren-match`

[tpapp]

Given that a single character is highlighted (the matching paren), alum1 is not very visible. Eg

(set-face-attribute 'show-paren-match nil :background "#e9b96e")

looks better.

[dgutov]

As a counterpoint, I sometimes think it's too visible. But most of the time, it's about right.