Fix DHH duplicate contributor entries

Map lowercase 'dhh' to 'David Heinemeier Hansson' to consolidate
the 5 commits authored as 'dhh' with the main contributor profile.

This fixes the issue where DHH appeared twice on contributors.rubyonrails.org:
- https://contributors.rubyonrails.org/contributors/dhh/commits (5 commits)
- https://contributors.rubyonrails.org/contributors/david-heinemeier-hansson/commits (4910 commits)

The mapping already included 'DHH' (uppercase) but was missing 'dhh' (lowercase).

Author: harsh183

app/models/names_manager/canonical_names.rb

@@ -359,7 +359,7 @@ def self.map(canonical_name, *also_as)
     map 'David Easley',               "easleydp\100gmail.com"
     map 'David Felstead',             "david.felstead\100gmail.com", "dfelstead\100site5.com"
     map 'David François',             'David FRANCOIS', 'davout'
-    map 'David Heinemeier Hansson',   'DHH', 'David' # for David see 5d5f0bad6e934d9d4fad7d0fa4643d04c13709a9
+    map 'David Heinemeier Hansson',   'DHH', 'dhh', 'David' # for David see 5d5f0bad6e934d9d4fad7d0fa4643d04c13709a9
     map 'David Morton',               "mortonda\100dgrmm.net"
     map 'David N. Welton',            'davidw'
     map 'David Raynes',               'rayners'

test/credits/canonical_names_test.rb

@@ -5159,5 +5159,9 @@ class CanonicalNamesTest < ActiveSupport::TestCase
     test 'प्रथमेश Sonpatki' do
       assert_contributor_names 'a7a2bc0f66', 'Prathamesh Sonpatki'
     end
+
+    test 'dhh' do
+      assert_contributor_names 'dd6f3e1', 'David Heinemeier Hansson'
+    end
   end
 end