Update babylon.tools.ts

Changing variable type from String to string (prevents warnings in the playground)

src/Tools/babylon.tools.ts

@@ -540,7 +540,7 @@
             }
         }
 
-        public static DumpFramebuffer(width: number, height: number, engine: Engine, successCallback?: (data: String) => void): void {
+        public static DumpFramebuffer(width: number, height: number, engine: Engine, successCallback?: (data: string) => void): void {
             // Read the contents of the framebuffer
             var numberOfChannelsByLine = width * 4;
             var halfHeight = height / 2;
@@ -606,7 +606,7 @@
             }
         }
 
-        public static CreateScreenshot(engine: Engine, camera: Camera, size: any, successCallback?: (data: String) => void): void {
+        public static CreateScreenshot(engine: Engine, camera: Camera, size: any, successCallback?: (data: string) => void): void {
             var width: number;
             var height: number;