Remove dependency to mruby-sprintf (Fix #3)

mrbgem.rake

@@ -2,7 +2,6 @@ MRuby::Gem::Specification.new('mruby-set') do |spec|
   spec.license = 'MIT'
   spec.authors = 'yui-knk'
 
-  spec.add_dependency "mruby-sprintf", :core => "mruby-sprintf"
   spec.add_dependency "mruby-hash-ext", :core => "mruby-hash-ext"
   spec.add_dependency "mruby-enumerator", :core => "mruby-enumerator"
 end

mrblib/mrb_set.rb

@@ -307,7 +307,7 @@ class Set
   end
 
   def inspect
-    sprintf('#<%s: {%s}>', self.class, to_a.inspect[1..-2])
+    "#<#{self.class}: {#{self.to_a.inspect[1..-2]}}>"
   end
 
 end