doc: Bump minimal Perl version to 5.14.2

The current version in Debian oldstable (wheezy) is 5.14.2.

doc/coding-style.txt

@@ -207,7 +207,7 @@ see what operation is being done:
 		foo();
 
 
-Dpkg Perl coding style 2013-01-04
+Dpkg Perl coding style 2015-05-20
 ======================
 
 General
@@ -244,7 +244,7 @@ Perl version
 
 We don't want to impose a too-recent Perl version, so only use features
 supported by the Perl version that is currently in Debian oldstable when
-possible. Currently that means Perl 5.10.0.
+possible. Currently that means Perl 5.14.2.
 
 Object methods
 ~~~~~~~~~~~~~~