disable grammarly, closes #733

src/components/content.js

@@ -860,6 +860,10 @@ class Content extends React.Component {
         style={style}
         role={readOnly ? null : (role || 'textbox')}
         tabIndex={tabIndex}
+        // COMPAT: The Grammarly Chrome extension works by changing the DOM out
+        // from under `contenteditable` elements, which leads to weird behaviors
+        // so we have to disable it like this. (2017/04/24)
+        data-gramm={false}
       >
         {children}
         {this.props.children}