Prepare for TypeScript 3.7

Summary:
These are the only four errors currently happening when upgrading to the 3.7 beta.
Luckily, these are all forwards-compatible changes.

Reviewed By: jknoxville

Differential Revision: D17711797

fbshipit-source-id: 429036e90300c81848cc3252b67bb89871ff2e32

src/chrome/LocationsButton.tsx

@@ -99,9 +99,9 @@ class LocationsButton extends Component<Props, State> {
     });
   };
 
-  componentDidMount = () => {
+  componentDidMount() {
     this.updateBookmarks();
-  };
+  }
 
   render() {
     const {currentURI} = this.props;