Fix React warnings for uppercase HTML heading elements (#373)

* Minor README spacing fix

* Prevent console spam on uppercase heading element

Author: Conrad2134

README.md

@@ -272,7 +272,7 @@ export default class extends Component {
 
 Here is where you can use the library's tags to compose your presentation. While you can use any JSX syntax here, building your presentation with the supplied tags allows for theming to work properly.
 
-The bare minimum you need to start is a`Deck` element and a `Slide` element. Each `Slide` element represents a slide inside of your slideshow.
+The bare minimum you need to start is a `Deck` element and a `Slide` element. Each `Slide` element represents a slide inside of your slideshow.
 
 <a name="themes"></a>
 ### Themes

src/components/__snapshots__/heading.test.js.snap

@@ -5,7 +5,7 @@ exports[`<Heading /> should render correctly. 1`] = `
   lineHeight={1}
   size={2}
 >
-  <H2
+  <h2
     className={undefined}
     data-radium={true}
     style={
@@ -16,7 +16,7 @@ exports[`<Heading /> should render correctly. 1`] = `
     }
   >
     Hi There!
-  </H2>
+  </h2>
 </Heading>
 `;
 

src/components/heading.js

@@ -41,7 +41,7 @@ export default class Heading extends Component {
   }
   render() {
     const { size, lineHeight, fit, style, children } = this.props;
-    const Tag = `H${size}`;
+    const Tag = `h${size}`;
     const styles = {
       container: {
         display: 'block',