make newline optional at the end of codeblocks

lib/rundoc/parser.rb

@@ -2,7 +2,7 @@ module Rundoc
   class Parser
     DEFAULT_KEYWORD = ":::"
     INDENT_BLOCK = '(?<before_indent>(^\s*$\n|\A)(^(?:[ ]{4}|\t))(?<indent_contents>.*)(?<after_indent>[^\s].*$\n?(?:(?:^\s*$\n?)*^(?:[ ]{4}|\t).*[^\s].*$\n?)*))'
-    GITHUB_BLOCK = '^(?<fence>(?<fence_char>~|`){3,})\s*?(?<lang>\w+)?\s*?\n(?<contents>.*?)^\g<fence>\g<fence_char>*\s*?\n'
+    GITHUB_BLOCK = '^(?<fence>(?<fence_char>~|`){3,})\s*?(?<lang>\w+)?\s*?\n(?<contents>.*?)^\g<fence>\g<fence_char>*\s*?\n?'
     CODEBLOCK_REGEX = /(#{GITHUB_BLOCK})/m
     COMMAND_REGEX = ->(keyword) {
       /^#{keyword}(?<tag>(\s|=|-|>)?(=|-|>)?)\s*(?<command>(\S)+)\s+(?<statement>.*)$/

test/rundoc/regex_test.rb

@@ -190,4 +190,26 @@ def test_complex_regex
 
     assert_equal contents.strip, match.to_s.strip
   end
+
+  def test_codeblock_optional_newline_regex
+    code_block_with_newline = <<~MD
+      hi
+      ```
+      :::>> $ echo "hello"
+      ```
+    MD
+    code_block_without_newline = code_block_with_newline.strip
+
+    expected = <<~MD.strip
+      ```
+      :::>> $ echo "hello"
+      ```
+    MD
+    regex = Rundoc::Parser::CODEBLOCK_REGEX
+    match = code_block_with_newline.match(regex)
+    assert_equal expected, match.to_s.strip
+
+    match = code_block_without_newline.match(regex)
+    assert_equal expected, match.to_s.strip
+  end
 end