Fix typo to 'prerequisites' link (GoogleCloudPlatform#369)

Author: wanacode

speech/README.md

@@ -27,7 +27,7 @@ recognition technologies into developer applications.
 
  yarn install
 
-[prereq]: ../README.md#prerequisities
+[prereq]: ../README.md#prerequisites
 [run]: ../README.md#how-to-run-a-sample
 
 ## Samples