fix(demos): Fix closing HTML tags in typography demo (#199)

demos/typography.html

@@ -38,10 +38,10 @@ <h1 class="mdc-typography--display4">Display 4</h1>
         <h1 class="mdc-typography--display3">Display 3</h1>
         <h1 class="mdc-typography--display2">Display 2</h1>
         <h1 class="mdc-typography--display1">Display 1</h1>
-        <h1 class="mdc-typography--headline">Headline</h2>
+        <h1 class="mdc-typography--headline">Headline</h1>
         <h2 class="mdc-typography--title">
           Title <span class="mdc-typography--caption">Caption.</span>
-        </h3>
+        </h2>
         <h3 class="mdc-typography--subheading2">Subheading 2</h3>
         <h4 class="mdc-typography--subheading1">Subheading 1</h4>
         <p class="mdc-typography--body1">Body 1 paragraph. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed
@@ -57,10 +57,10 @@ <h1 class="mdc-typography--display4 mdc-typography--adjust-margin">Display 4</h1
         <h1 class="mdc-typography--display3 mdc-typography--adjust-margin">Display 3</h1>
         <h1 class="mdc-typography--display2 mdc-typography--adjust-margin">Display 2</h1>
         <h1 class="mdc-typography--display1 mdc-typography--adjust-margin">Display 1</h1>
-        <h1 class="mdc-typography--headline mdc-typography--adjust-margin">Headline</h2>
+        <h1 class="mdc-typography--headline mdc-typography--adjust-margin">Headline</h1>
         <h2 class="mdc-typography--title mdc-typography--adjust-margin">
           Title <span class="mdc-typography--caption mdc-typography--adjust-margin">Caption.</span>
-        </h3>
+        </h2>
         <h3 class="mdc-typography--subheading2 mdc-typography--adjust-margin">Subheading 2</h3>
         <h4 class="mdc-typography--subheading1 mdc-typography--adjust-margin">Subheading 1</h4>
         <p class="mdc-typography--body1 mdc-typography--adjust-margin">Body 1 paragraph. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed