pandocomatic: Use language-specific heredocs

Author: issyl0

Formula/p/pandocomatic.rb

@@ -45,11 +45,11 @@ def install
   end
 
   test do
-    (testpath/"test.md").write <<~EOS
+    (testpath/"test.md").write <<~MARKDOWN
       # Homebrew
 
       A package manager for humans. Cats should take a look at Tigerbrew.
-    EOS
+    MARKDOWN
     expected_html = <<~EOS
       <h1 id="homebrew">Homebrew</h1>
       <p>A package manager for humans. Cats should take a look at