Avoid hash as a variable name

Not sure using `hash` poses any risk, but the Ruby docs use `h` or
`hsh`:

http://www.ruby-doc.org/core-2.1.5/Hash.html

lib/ransack/adapters/active_record/3.0/compat.rb

@@ -121,11 +121,11 @@ module Arel
       end
 
       def column_cache
-        @column_cache ||= Hash.new do |hash, key|
-          hash[key] = Hash[
-            @engine.connection.columns(key, "#{key} Columns").map do |c|
-              [c.name, c]
-            end
+        @column_cache ||= Hash.new do |h, key|
+          h[key] = Hash[
+            @engine.connection
+            .columns(key, "#{key} Columns")
+            .map { |c| [c.name, c] }
           ]
         end
       end

lib/ransack/adapters/active_record/ransack/context.rb

@@ -39,10 +39,10 @@ module Ransack
       @default_table = Arel::Table.new(
         @base.table_name, :as => @base.aliased_table_name, :engine => @engine
         )
-      @bind_pairs = Hash.new do |hash, key|
+      @bind_pairs = Hash.new do |h, key|
         parent, attr_name = get_parent_and_attribute_name(key.to_s)
         if parent && attr_name
-          hash[key] = [parent, attr_name]
+          h[key] = [parent, attr_name]
         end
       end
     end

lib/ransack/adapters/mongoid/ransack/context.rb

@@ -34,10 +34,10 @@ module Ransack
       # @default_table = Arel::Table.new(
       #   @base.table_name, :as => @base.aliased_table_name, :engine => @engine
       #   )
-      @bind_pairs = Hash.new do |hash, key|
+      @bind_pairs = Hash.new do |h, key|
         parent, attr_name = get_parent_and_attribute_name(key.to_s)
         if parent && attr_name
-          hash[key] = [parent, attr_name]
+          h[key] = [parent, attr_name]
         end
       end
     end

lib/ransack/visitor.rb

@@ -52,8 +52,8 @@ module Ransack
       send(DISPATCH[object.class], object)
     end
 
-    DISPATCH = Hash.new do |hash, klass|
-      hash[klass] = "visit_#{
+    DISPATCH = Hash.new do |h, klass|
+      h[klass] = "visit_#{
         klass.name.gsub(Constants::TWO_COLONS, Constants::UNDERSCORE)
         }"
     end