add missing word in 03_runtime.md (#259)

Improved phrasing for  the `scope` h2

book/src/07_threads/04_scoped_threads.md

@@ -27,7 +27,7 @@ Let's unpack what's happening.
 ## `scope`
 
 The `std::thread::scope` function creates a new **scope**.\
-`std::thread::scope` takes as input a closure, with a single argument: a `Scope` instance.
+`std::thread::scope` takes a closure as input, with a single argument: a `Scope` instance.
 
 ## Scoped spawns
 

book/src/08_futures/03_runtime.md

@@ -26,7 +26,7 @@ at any given time.
 
 ### Multithreaded runtime
 
-When using the multithreaded runtime, instead, there can up to `N` tasks running
+When using the multithreaded runtime, instead, there can be up to `N` tasks running
 _in parallel_ at any given time, where `N` is the number of threads used by the
 runtime. By default, `N` matches the number of available CPU cores.