Handle Office Open XML types for filed generated outside MSOffice

It turns out that the position of '[Content_Types].xml' is not fixed in
this format, and whereas MS Office adds it in the beginning in general,
when files are generated using Google Docs, or RubyXL, this is not
necessarily true. They might add it at the end, so all these would be
detected as application/zip.

This fixes #39

lib/mimemagic/overlay.rb

 # Extra magic
 
-[['application/vnd.openxmlformats-officedocument.presentationml.presentation', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..5000, 'ppt/']]]]]]],
- ['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..5000, 'xl/']]]]]]],
- ['application/vnd.openxmlformats-officedocument.wordprocessingml.document', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..5000, 'word/']]]]]]]].each do |magic|
+[['application/vnd.openxmlformats-officedocument.presentationml.presentation', [[0, "PK\003\004", [[0..5000, '[Content_Types].xml', [[0..5000, 'ppt/']]]]]]],
+ ['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', [[0, "PK\003\004", [[0..5000, '[Content_Types].xml', [[0..5000, 'xl/']]]]]]],
+ ['application/vnd.openxmlformats-officedocument.wordprocessingml.document', [[0, "PK\003\004", [[0..5000, '[Content_Types].xml', [[0..5000, 'word/']]]]]]]].each do |magic|
   MimeMagic.add(magic[0], magic: magic[1])
 end

test/mimemagic_test.rb

@@ -70,14 +70,17 @@ class TestMimeMagic < Minitest::Test
 
   def test_recognize_xlsx_as_zip_without_magic
     file = "test/files/application.vnd.openxmlformats-officedocument.spreadsheetml.sheet"
-    assert_equal "application/zip", MimeMagic.by_magic(File.read(file)).to_s
-    assert_equal "application/zip", MimeMagic.by_magic(File.open(file, 'rb')).to_s
+    %w(msoffice rubyxl gdocs).each do |variant|
+      file = "test/files/application.vnd.openxmlformats-officedocument.spreadsheetml{#{variant}}.sheet"
+      assert_equal "application/zip", MimeMagic.by_magic(File.read(file)).to_s
+      assert_equal "application/zip", MimeMagic.by_magic(File.open(file, 'rb')).to_s
+    end
   end
 
   def test_recognize_by_magic
     load "mimemagic/overlay.rb"
     Dir['test/files/*'].each do |file|
-      mime = file[11..-1].sub('.', '/')
+      mime = file[11..-1].sub('.', '/').sub(/\{\w+\}/, '')
       assert_equal mime, MimeMagic.by_magic(File.read(file)).to_s
       assert_equal mime, MimeMagic.by_magic(File.open(file, 'rb')).to_s
     end
@@ -85,9 +88,11 @@ class TestMimeMagic < Minitest::Test
 
   def test_recognize_all_by_magic
     load 'mimemagic/overlay.rb'
-    file = 'test/files/application.vnd.openxmlformats-officedocument.spreadsheetml.sheet'
-    mimes = %w[application/vnd.openxmlformats-officedocument.spreadsheetml.sheet application/zip]
-    assert_equal mimes, MimeMagic.all_by_magic(File.read(file)).map(&:type)
+    %w(msoffice rubyxl gdocs).each do |variant|
+      file = "test/files/application.vnd.openxmlformats-officedocument.spreadsheetml{#{variant}}.sheet"
+      mimes = %w[application/vnd.openxmlformats-officedocument.spreadsheetml.sheet application/zip]
+      assert_equal mimes, MimeMagic.all_by_magic(File.read(file)).map(&:type)
+    end
   end
 
   def test_have_add