Fixed typos on block api documentation (#11298)

* merge from upstream

* fixed typos in block API documentation

docs/block-api.md

@@ -140,7 +140,7 @@ styles: [
 ],
 ```
 
-Plugins and Themes can also register [custom block style](../docs/extensibility/extending-blocks/#block-style-variations) for exisiting blocks.
+Plugins and Themes can also register [custom block style](../docs/extensibility/extending-blocks/#block-style-variations) for existing blocks.
 
 #### Attributes (optional)
 
@@ -490,7 +490,7 @@ className: false,
 html: false,
 ```
 
-- `inserter` (default `true`): By default, all blocks will appear in the Gutenberg inserter. To hide a block so that it can only be inserted programatically, set `inserter` to `false`.
+- `inserter` (default `true`): By default, all blocks will appear in the Gutenberg inserter. To hide a block so that it can only be inserted programmatically, set `inserter` to `false`.
 
 ```js
 // Hide this block from the inserter.