Patch Ancestry::InstanceMethods#parse_ancestry_column

Calls `.map!` instead of `.map` since we already have a temp array from
the `.split`, and this avoids creating a completely new array for the
second time in this method.

* * *

Before/After
------------

Total allocated: 318431331 bytes (2943673 objects)   |   Total allocated: 316196585 bytes (2917071 objects)
                                                     |
allocated objects by gem                             |   allocated objects by gem
-----------------------------------                  |   -----------------------------------
   1576834  activerecord-5.0.7                       |      1576834  activerecord-5.0.7
    477120  manageiq/app                             |       477120  manageiq/app
    274449  activemodel-5.0.7                        |       274449  activemodel-5.0.7
    267060  ancestry-2.2.2  <<<<<<<<<<               |       208479  manageiq/lib
    106559  activesupport-5.0.7                      |       106557  activesupport-5.0.7
     82799  pending                                  |        82799  pending
     74117  ruby-2.3.3/lib                           |        74117  ruby-2.3.3/lib
     52875  manageiq-providers-vmware-0be2f13a0dc9   |        52875  manageiq-providers-vmware-0be2f13a0dc9
     14424  fast_gettext-1.2.0                       |        35578  ancestry-2.2.2  <<<<<<<<<<
     ...                                             |        ...

lib/patches/ancestry_patch.rb

@@ -1,6 +1,10 @@
 module Ancestry
   module InstanceMethods
 
+    def parse_ancestry_column obj
+      obj.to_s.split('/').map! { |id| cast_primary_key(id) }
+    end
+
     STRING_BASED_KEYS = [:string, :uuid, :text].freeze
     def cast_primary_key(key)
       if STRING_BASED_KEYS.include? primary_key_type