docs(cdk/scrolling): small fixes (angular#10432)

Re-wording of the 1st sentence in ###. I guess this is the correct meaning of what was wanted.

src/cdk/scrolling/scrolling.md

@@ -1,7 +1,7 @@
 The `scrolling` package provides helpers for directives that react to scroll events.
 
 ### cdkScrollable and ScrollDispatcher
-The `cdkScrollable` directive and the `ScrollDispatcher` service to together to allow components to
+The `cdkScrollable` directive and the `ScrollDispatcher` service together allow components to
 react to scrolling in any of its ancestor scrolling containers.
 
 The `cdkScrollable` directive should be applied to any element that acts as a scrolling container.