Use unpack1 instead of unpack and first

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57588 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/base64.rb

@@ -56,7 +56,7 @@ module Base64
   #    This is line three
   #    And so on...
   def decode64(str)
-    str.unpack("m").first
+    str.unpack1("m")
   end
 
   # Returns the Base64-encoded version of +bin+.
@@ -71,7 +71,7 @@ module Base64
   # ArgumentError is raised if +str+ is incorrectly padded or contains
   # non-alphabet characters.  Note that CR or LF are also rejected.
   def strict_decode64(str)
-    str.unpack("m0").first
+    str.unpack1("m0")
   end
 
   # Returns the Base64-encoded version of +bin+.