Add "mruby developers" into some gems; Resolve #4709

It is writing side by side with the original authors.

mrbgems/mruby-io/README.md

@@ -171,6 +171,7 @@ Add the line below to your `build_config.rb`:
 ## License
 
 Copyright (c) 2013 Internet Initiative Japan Inc.
+Copyright (c) 2017 mruby developers
 
 Permission is hereby granted, free of charge, to any person obtaining a 
 copy of this software and associated documentation files (the "Software"), 

mrbgems/mruby-io/mrbgem.rake

 MRuby::Gem::Specification.new('mruby-io') do |spec|
   spec.license = 'MIT'
-  spec.authors = 'Internet Initiative Japan Inc.'
+  spec.authors = ['Internet Initiative Japan Inc.', 'mruby developers']
   spec.summary = 'IO and File class'
 
   spec.cc.include_paths << "#{build.root}/src"

mrbgems/mruby-pack/README.md

@@ -49,6 +49,7 @@ There is no dependency on other mrbgems.
 ## License
 
 Copyright (c) 2012 Internet Initiative Japan Inc.
+Copyright (c) 2017 mruby developers
 
 Permission is hereby granted, free of charge, to any person obtaining a 
 copy of this software and associated documentation files (the "Software"), 

mrbgems/mruby-pack/mrbgem.rake

 MRuby::Gem::Specification.new('mruby-pack') do |spec|
   spec.license = 'MIT'
-  spec.authors = 'Internet Initiative Japan Inc.'
+  spec.authors = ['Internet Initiative Japan Inc.', 'mruby developers']
   spec.summary = 'Array#pack and String#unpack method'
 
   spec.cc.include_paths << "#{build.root}/src"

mrbgems/mruby-sleep/mrbgem.rake

 MRuby::Gem::Specification.new('mruby-sleep') do |spec|
   spec.license = 'MIT'
-  spec.authors = 'MATSUMOTO Ryosuke'
+  spec.authors = ['MATSUMOTO Ryosuke', 'mruby developers']
   spec.version = '0.0.1'
 end

mrbgems/mruby-sleep/src/mrb_sleep.c

@@ -2,6 +2,7 @@
 ** mrb_sleep - sleep methods for mruby
 **
 ** Copyright (c) mod_mruby developers 2012-
+** Copyright (c) mruby developers 2018
 **
 ** Permission is hereby granted, free of charge, to any person obtaining
 ** a copy of this software and associated documentation files (the

mrbgems/mruby-socket/README.md

@@ -35,6 +35,7 @@ Date: Tue, 21 May 2013 04:31:30 GMT
 ## License
 
 Copyright (c) 2013 Internet Initiative Japan Inc.
+Copyright (c) 2017 mruby developers
 
 Permission is hereby granted, free of charge, to any person obtaining a
 copy of this software and associated documentation files (the "Software"),

mrbgems/mruby-socket/mrbgem.rake

 MRuby::Gem::Specification.new('mruby-socket') do |spec|
   spec.license = 'MIT'
-  spec.authors = 'Internet Initiative Japan'
+  spec.authors = ['Internet Initiative Japan', 'mruby developers']
   spec.summary = 'standard socket class'
 
   spec.cc.include_paths << "#{build.root}/src"