Migrate deprecated show-paren-X-face faces (#89)

The `show-paren-match-face` and `show-paren-mismatch-face` face are
deprecated since Emacs version 22.1 [1,2] and were removed in Emacs 25.
To provide compatibilty to later EMacs version, the new
`show-paren-match` and `show-paren-mismatch` faces have been added.

The deprecated faces will be removed later on, but for now its totally
fine for both faces to co-exist to support Emacs versions <22.1 as well
as >=22.1.

[1]: http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=c430f7e23fc2c22f251ace4254e37dea1452dfc3
[2]: emacs-mirror/emacs@c430f7e

Closes GH-75

nord-theme.el

@@ -275,8 +275,17 @@
     `(region ((,class (:foreground ,nord-region-highlight-foreground :background ,nord-region-highlight-background))))
     `(scroll-bar ((,class (:background ,nord3))))
     `(secondary-selection ((,class (:background ,nord2))))
+
+    ;; `show-paren-match-face` and `show-paren-mismatch-face` are deprecated since Emacs version 22.1 and were
+    ;; removed in Emacs 25.
+    ;; https://github.com/arcticicestudio/nord-emacs/issues/75
+    ;; http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=c430f7e23fc2c22f251ace4254e37dea1452dfc3
+    ;; https://github.com/emacs-mirror/emacs/commit/c430f7e23fc2c22f251ace4254e37dea1452dfc3
     `(show-paren-match-face ((,class (:foreground ,nord0 :background ,nord8))))
     `(show-paren-mismatch-face ((,class (:background ,nord11))))
+
+    `(show-paren-match ((,class (:foreground ,nord0 :background ,nord8))))
+    `(show-paren-mismatch ((,class (:background ,nord11))))
     `(success ((,class (:foreground ,nord14))))
     `(term ((,class (:foreground ,nord4 :background ,nord0))))
     `(term-color-black ((,class (:foreground ,nord1 :background ,nord1))))