make javadocs for scan() more precise (#1857)

Author: DavidMGross

src/main/java/rx/Observable.java

@@ -6470,7 +6470,7 @@ public final <U> Observable<T> sample(Observable<U> sampler) {
     }
 
     /**
-     * Returns an Observable that applies a function of your choosing to the first item emitted by a source
+     * Returns an Observable that applies a specified accumulator function to the first item emitted by a source
      * Observable, then feeds the result of that function along with the second item emitted by the source
      * Observable into the same function, and so on until all items have been emitted by the source Observable,
      * emitting the result of each of these iterations.
@@ -6496,7 +6496,7 @@ public final Observable<T> scan(Func2<T, T, T> accumulator) {
     }
 
     /**
-     * Returns an Observable that applies a function of your choosing to the first item emitted by a source
+     * Returns an Observable that applies a specified accumulator function to the first item emitted by a source
      * Observable and a seed value, then feeds the result of that function along with the second item emitted by
      * the source Observable into the same function, and so on until all items have been emitted by the source
      * Observable, emitting the result of each of these iterations.
@@ -6528,7 +6528,7 @@ public final <R> Observable<R> scan(R initialValue, Func2<R, ? super T, R> accum
     }
 
     /**
-     * Returns an Observable that applies a function of your choosing to the first item emitted by a source
+     * Returns an Observable that applies a specified accumulator function to the first item emitted by a source
      * Observable and a seed value, then feeds the result of that function along with the second item emitted by
      * the source Observable into the same function, and so on until all items have been emitted by the source
      * Observable, emitting the result of each of these iterations.