Replace unicode MINUS SIGN with ascii HYPHEN-MINUS

Perldoc shows a pod error:
  Hey! The above document had some coding errors, which are explained below:
  Non-ASCII character seen before =encoding in ''<:encoding(UTF−8)');'. Assuming UTF-8

Trying the verbatim code throws an exception:
  Cannot find encoding "UTF−8" at /home/rando/perl5/perlbrew/perls/5.14.2-st/lib/5.14.2/x86_64-linux-thread-multi/IO/File.pm line 182.
Merge pull request #13 from rwstauner/master

Replace unicode MINUS SIGN with ascii HYPHEN-MINUS