FIX: Inline error when converting html to markdown

Looks like some html elements like `aside` and `section` will throw an error
when checking if they are inline or not. The commit simply handles

```
Job exception: undefined method `inline?' for nil:NilClass
```

and adds a test for it.

lib/html_to_markdown.rb

@@ -99,7 +99,7 @@ class HtmlToMarkdown
   end
 
   def is_inline?(node)
-    node.text? || ("br" != node.name && node.description.inline? && node.children.all? { |n| is_inline?(n) })
+    node.text? || ("br" != node.name && node.description&.inline? && node.children.all? { |n| is_inline?(n) })
   end
 
   def collapse_spaces!(nodes, was_space = true)

spec/components/html_to_markdown_spec.rb

@@ -65,6 +65,23 @@ describe HtmlToMarkdown do
     expect(html_to_markdown(html)).to eq(markdown.strip)
   end
 
+  it "doesn't error on non-inline elements like (aside, section)" do
+
+    html = <<~HTML
+      <aside class="quote no-group">
+      <blockquote>
+      <p>hello.</p>
+      </blockquote>
+      </aside>
+    HTML
+
+    markdown = <<~MD
+      > hello.
+    MD
+
+    expect(html_to_markdown(html)).to eq(markdown.strip)
+  end
+
   it "skips hidden tags" do
     expect(html_to_markdown(%Q{<p>Hello <span style="display: none">cruel </span>World!</p>})).to eq("Hello World!")
     expect(html_to_markdown(%Q{<p>Hello <span hidden>cruel </span>World!</p>})).to eq("Hello World!")