Support new spreadsheet

Hello, lopnor.
I tried to use Net::Google::Spreadsheets with New Google Spreadsheet.

``` perl
my $service = Net::Google::Spreadsheets->new(auth => $auth);

# '1Y-xxxxxxxxxxxxxxxxxxxxxxxxxxxxx' is New Google Spreadsheet
my $spreadsheet = $service->spreadsheet({key => '1Y-xxxxxxxxxxxxxxxxxxxxxxxxxxxxx'});
```

but I got some warnings and it didn't work.

``` plain
Use of uninitialized value $nsURI in string eq at /home/ichinose/.plenv/versions/5.18.2/lib/perl5/site_perl/5.18.2/x86_64-linux/XML/LibXML.pm line 1702.
Use of uninitialized value $nsURI in concatenation (.) or string at /home/ichinose/.plenv/versions/5.18.2/lib/perl5/site_perl/5.18.2/x86_64-linux/XML/LibXML.pm line 1705.
```

it seems that `https://spreadsheets.google.com/feeds/spreadsheets/private/full?key={key}` doesn't work if the key is for New Google Spreadsheet.
I changed that it gets an entry of spreadsheet from specific URL if key is passed.
(see also: https://github.com/gimite/google-drive-ruby)