Coroutines Method Typo (#1385)

Summary:
The `collectSemiFuture` method doesn't exist.  Use `collectAllSemiFuture` instead.
Pull Request resolved: https://github.com/facebook/folly/pull/1385

Reviewed By: yfeldblum

Differential Revision: D21991532

Pulled By: DerekTBrown

fbshipit-source-id: 4ba3378fe34b7e6bb910f7045267fdbab87ebb14

folly/experimental/coro/README.md

@@ -332,7 +332,7 @@ folly::coro::Task<void> example(int count) {
   for (int i = 0; i < count; ++i) {
     tasks.push_back(doWork(i).semi());
   }
-  co_await folly::collectSemiFuture(tasks.begin(), tasks.end());
+  co_await folly::collectAllSemiFuture(tasks.begin(), tasks.end());
 }
 ```
 
@@ -348,8 +348,8 @@ folly::coro::Task<void> example(int count) {
 
   // Concurrently wait for all of these tasks.
   std::vector<std::string> strings =
-      co_await folly::collectSemiFuture(tasks.begin(), tasks.end());
+      co_await folly::collectAllSemiFuture(tasks.begin(), tasks.end());
 
   // ... use 'strings'
 }
-```
\ No newline at end of file
+```