Fix: Faker::Number.hexadecimal should include characters within the range of [0-9a-f] (#2942)

* Include 'f' character within Faker::Number.hexadecimal

Author: alextaujenis

lib/faker/default/number.rb

@@ -114,7 +114,7 @@ def digit
       # @faker.version 1.0.0
       def hexadecimal(digits: 6)
         hex = ''
-        digits.times { hex += rand(15).to_s(16) }
+        digits.times { hex += rand(16).to_s(16) }
         hex
       end
 

test/faker/default/test_faker_number.rb

@@ -130,6 +130,13 @@ def test_hexadecimal
     assert_match(/[0-9a-f]{7}/, @tester.hexadecimal(digits: 7))
   end
 
+  def test_hexadecimal_range
+    random_hex = @tester.hexadecimal(digits: 1000)
+    expected_range = Array('0'..'9') + Array('a'..'f')
+
+    expected_range.each { |char| assert_include(random_hex, char) }
+  end
+
   def test_binary
     assert_match(/^[0-1]{4}$/, @tester.binary(digits: 4))
     assert_match(/^[0-1]{8}$/, @tester.binary(digits: 8))