Fix default value of electric-pair-pairs and electric-pair-text-pairs

Fix default value of electric-pair-pairs and electric-pair-text-pairs

Fixes: debbugs:24901
A previous change, titled "Add support for curly quotation marks to
electric-pair-mode", attempted to add these characters to the default
value of these variables.  But it did so in a quoted list, preventing
evaluation of the relevant expressions and resulting in an invalid
format.

* lisp/elec-pair.el (electric-pair-pairs, electric-pair-text-pairs):
Use backquote and comma.