rename Relation#shift to padding

bacause this method name was turned out to be stubbing out Array#shift

README.rdoc

@@ -63,11 +63,11 @@ Then bundle:
     User.page(7).per(50)
   Note that the +per+ scope is not directly defined on the models but is just a method defined on the page scope. This is absolutely reasonable because you will never actually use +per_page+ without specifying the +page+ number.
 
-* the +shift+ scope
+* the +padding+ scope
 
-  Occasionally you need to shift a number of records that is not a multiple of the page size.
-    User.page(7).per(50).shift(3)
-  Note that the +shift+ scope is not directly defined on the models but is just a method defined on the page scope. This is absolutely reasonable because you can use +offset+ otherwise.
+  Occasionally you need to padding a number of records that is not a multiple of the page size.
+    User.page(7).per(50).padding(3)
+  Note that the +padding+ scope is not directly defined on the models but is just a method defined on the page scope. This is absolutely reasonable because you can use +offset+ otherwise.
 
 === General configuration options
 

lib/kaminari/models/page_scope_methods.rb

@@ -12,7 +12,7 @@ module Kaminari
         end
       end
 
-      def shift(num)
+      def padding(num)
         offset(offset_value + num.to_i)
       end
 

spec/models/scopes_spec.rb

@@ -58,9 +58,9 @@ describe Kaminari::ActiveRecordExtension do
         end
       end
 
-      describe '#shift' do
-        context 'page 1 per 5 shift 1' do
-          subject { model_class.page(1).per(5).shift(1) }
+      describe '#padding' do
+        context 'page 1 per 5 padding 1' do
+          subject { model_class.page(1).per(5).padding(1) }
           it { should have(5).users }
           its('first.name') { should == 'user002' }
         end