fix Builder#initialize with block

lib/faraday/builder.rb

@@ -52,7 +52,7 @@ module Faraday
     def initialize(handlers = [])
       @handlers = handlers
       @inner_app = self.class.inner_app
-      build(Proc.new) if block_given?
+      build(&Proc.new) if block_given?
     end
 
     def build(options = {})

lib/faraday/connection.rb

@@ -33,9 +33,7 @@ module Faraday
       merge_headers @headers, options[:headers] if options[:headers]
 
       if block_given?
-        block    = Proc.new
-        @builder = Builder.new
-        @builder.build { block.call(self) }
+        @builder = Builder.create { |b| yield b }
       else
         @builder = options[:builder] || Builder.new
       end