Corrected mistake

Author: saroamirkhanyan

manuscript/ch10.md

@@ -320,7 +320,7 @@ var b =
  .filter( v => v % 2 == 1 ) // only odd numbers
  .distinctUntilChanged() // only consecutive-distinct
  .throttle( 100 ) // slow it down a bit
- .map( v = v * 2 );  // double them
+ .map( v => v * 2 ); // double them
 
 b.subscribe( function onValue(v){
  console.log( "Next:", v );