contents(js): update use strict answer (#346)

contents/javascript-questions.md

@@ -751,7 +751,7 @@ Advantages:
 
 - Makes it impossible to accidentally create global variables.
 - Makes assignments which would otherwise silently fail to throw an exception.
-- Makes attempts to delete undeletable properties throw (where before the attempt would simply have no effect).
+- Makes attempts to delete undeletable properties throw an exception (where before the attempt would simply have no effect).
 - Requires that function parameter names be unique.
 - `this` is undefined in the global context.
 - It catches some common coding bloopers, throwing exceptions.