Depend on rubyzip, not zip

The 'zip' gem is unmaintained and obsolete. 'rubzip' is
the most popular and best supported zip gem for ruby.
It supports Ruby 1.9 and Windows.
Merge pull request #7 from Verba/rubyzip

Depend on rubyzip, not zip
allow crxmake to run in-place
Merge pull request #8 from t3rmin4t0r/master

Allow bin/crxmake to run in-place
Remove old zip file before making zip file.

If old zip file exist, zip.rb throw Zip::ZipEntryExistsError. Therefore CrxMake.zip cannot make new zip file.
In order to solve this problem, add remove old zip file function, before making it.

Remove zip file function is already inpremented in code.(function name = final) But, function name 'final' is not suitable for not final place.
So, I rename final to remove_zip.
Merge pull request #10 from samurai20000/zipexisterror

Remove old zip file before making zip file.
version 2.1.0
jruby friendly

Bug with OpenSSL::PKey::RSA.new
version 2.0.5
Merge pull request #11 from qwert666/master

Fix for jruby
version 2.1.1
Add license MIT
version 2.1.2
export pem in pkcs8 to relax Chrome WebStore
Merge pull request #13 from cielavenir/master

export pem in pkcs8 to relax Chrome WebStore
show warning only if verbose is set; no ways to suppress it on JRuby
Merge pull request #14 from cielavenir/master

show warning only if verbose is set; no ways to suppress it on JRuby
avoid creating temporary zip
Merge pull request #15 from cielavenir/master

avoid creating temporary zip
Merge remote-tracking branch 'origin/master'