Replace mimemagic with mime-types

This change is to avoid troubles due to the licensing issue of mimemagic.
See mimemagicrb/mimemagic#97 for the detail.

Author: mrkn

iruby.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'bond', '~> 0.5'
   s.add_dependency 'data_uri', '~> 0.1'
   s.add_dependency 'ffi-rzmq'
-  s.add_dependency 'mimemagic', '~> 0.3'
+  s.add_dependency 'mime-types', '>= 3.3.1'
   s.add_dependency 'multi_json', '~> 1.11'
 
   s.add_development_dependency 'pycall', '>= 1.2.1'

lib/iruby.rb

@@ -1,4 +1,4 @@
-require 'mimemagic'
+require 'mime/types'
 require 'multi_json'
 require 'securerandom'
 require 'openssl'

lib/iruby/display.rb

@@ -44,7 +44,7 @@ def clear_output(wait = false)
       private
 
       def protect(mime, data)
-        MimeMagic.new(mime).text? ? data.to_s : [data.to_s].pack('m0')
+        MIME::Type.new(mime).ascii? ? data.to_s : [data.to_s].pack('m0')
       end
 
       def render(data, obj, exact_mime, fuzzy_mime)
@@ -304,7 +304,7 @@ def format(mime = nil, &block)
 
       match { |obj| obj.respond_to?(:path) && obj.method(:path).arity == 0 && File.readable?(obj.path) }
       format do |obj|
-        mime = MimeMagic.by_path(obj.path).to_s
+        mime = MIME::Types.of(obj.path).first.to_s
         [mime, File.read(obj.path)] if SUPPORTED_MIMES.include?(mime)
       end