Fix GH #3743. We must specify an encoding in rdoc_option explicitly.

[kennyj]

We should specify an encoding in rdoc_option explicitly.
The encoding is not specified in activesupport.gemspec.

Before:

~/rails(fix_3743)$ export LANG=en_US.ISO-8859-1 ★ specified no UTF-8 encoding.
~/rails(fix_3743)$ cd (path to rails)
~/rails(fix_3743)$ rake build
~/rails(fix_3743)$ cd pkg
~/rails/pkg(fix_3743)$ gem install activesupport-4.0.0.beta.gem
Successfully installed activesupport-4.0.0.beta
1 gem installed
Installing ri documentation for activesupport-4.0.0.beta...
Installing RDoc documentation for activesupport-4.0.0.beta...
ERROR:  While generating documentation for activesupport-4.0.0.beta
... MESSAGE:   error generating ActiveSupport/Inflector.html: incompatible encoding regexp match (UTF-8 regexp with ISO-8859-1 string) (Encoding::CompatibilityError)
... RDOC args: --op /home/kennyj/.rvm/gems/ruby-1.9.3-p0/doc/activesupport-4.0.0.beta/rdoc lib --title activesupport-4.0.0.beta Documentation --quiet

After:

~/rails/pkg(fix_3743)$ gem install activesupport-4.0.0.beta.gem
Successfully installed activesupport-4.0.0.beta
1 gem installed
Installing ri documentation for activesupport-4.0.0.beta...
Installing RDoc documentation for activesupport-4.0.0.beta...
~/rails/pkg(fix_3743)$

Please see also #3743.

[kennyj]

@spastorino thanks merge it !

Should I send PR to 3-2 or 3-1 ?
The original issue is reported on 3.1.3.

[spastorino]

@kennyj I've backported it to both

[kennyj]

Oops.. I realized that you merged it on 3-2-stable and 3-1-stable. thanks.