scape left brace in regex.

[sebastic]

Quoting perldelta:

A literal "{" should now be escaped in a pattern

If you want a literal left curly bracket (also called a left brace) in
a regular expression pattern, you should now escape it by either
preceding it with a backslash ("{") or enclosing it within square
brackets "[{]", or by using \Q; otherwise a deprecation warning will be
raised. This was first announced as forthcoming in the v5.16 release;
it will allow future extensions to the language to happen.

http://search.cpan.org/dist/perl-5.22.0/pod/perldelta.pod#A_literal_%22{%22_should_now_be_escaped_in_a_pattern

Fixes #12