Fix version extraction to work with non ASCII characters with any LANG

d9fe72a introduced a non-ASCII character (U+2014) in comment but
Regex match failed with non UTF-8 locale.

This commit fixes it by specifying encoding explicitly.

net-smtp.gemspec

@@ -2,7 +2,7 @@
 
 name = File.basename(__FILE__, ".gemspec")
 version = ["lib", Array.new(name.count("-"), "..").join("/")].find do |dir|
-  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb")) do |line|
+  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb"), :encoding => "UTF-8") do |line|
     /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
   end rescue nil
 end