docs: typo Fixes (react-bootstrap#3472)

Fixes a few typos in some of the documentation on the site.

Author: teddim

src/Col.js

@@ -37,7 +37,7 @@ class Col extends React.Component {
     as: elementType,
 
     /**
-     * The number of columns to span on sxtra small devices (<576px)
+     * The number of columns to span on extra small devices (<576px)
      *
      * @type {(true|"auto"|number|{ span: true|"auto"|number, offset: number, order: number })}
      */

src/Container.js

@@ -13,7 +13,7 @@ class Container extends React.Component {
     bsPrefix: PropTypes.string,
 
     /**
-     * Allow the Container to fill all of it's availble horizontal space.
+     * Allow the Container to fill all of its available horizontal space.
      */
     fluid: PropTypes.bool,
     /**

www/src/pages/getting-started/introduction.mdx

@@ -19,7 +19,7 @@ The best way to consume React Bootstrap is via the npm package which
 you can install with `npm` (or yarn if you prefer).
 
 If you plan on customizing the Bootstrap Sass files, or don't want
-to use a CDN for the stylesheet, it may helpful to
+to use a CDN for the stylesheet, it may be helpful to
 install <DocLink path="/getting-started/download/#npm">vanilla Bootstrap</DocLink> as well.
 
 ```jsx