Add missing properties for GridTile component

types/material-ui/index.d.ts

@@ -8,6 +8,7 @@
 //                 Aurelién Allienne <https://github.com/allienna>
 //                 Matthias Schlesinger <https://github.com/schlesingermatthias>
 //                 Jonathon Kelly <https://github.com/InsidersByte>
+//                 Artyom Stukans <https://github.com/artyomsv>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -1057,6 +1058,7 @@ declare namespace __MaterialUI {
             title?: React.ReactNode;
             titleBackground?: string;
             titlePosition?: "top" | "bottom";
+            titleStyle?: React.CSSProperties;
             onTouchTap?: TouchTapEventHandler;
         }
         export class GridTile extends React.Component<GridTileProps> {