Bug#1013875: lintian: false-postive for experimental-to-unstable-without-comment

[Gioele Barabucci]

An alternative fix, suggested by dwfreed on #debian-qa, would be to add 
a `/x` modifier to the current regex in `Changelog.pm` (`/x` ignores 
whitespace in the regex, increasing its readability):

-  !~ m{ \b to \s+ ['"‘“]? (?:unstable|sid) ['"’”]? \b }im;
+  !~ m{ \b to \s+ ['"‘“]? (?:unstable|sid) ['"’”]? \b }imx;
Regards

--
Gioele Barabucci