Grammar mistake and docs build.

buildutils/README.md

@@ -3,4 +3,4 @@
 A JupyterLab package which provides utility functions that are used to compile
 and build JupyterLab.
 
-This package is only intended for use within a Node.js environments.
+This package is only intended for use within Node.js environments.

packages/coreutils/src/poll.ts

@@ -18,7 +18,7 @@ const defer =
 /**
  * A function to cancel a deferred action.
  */
-const cancel =
+const cancel: (timeout: any) => void =
   typeof cancelAnimationFrame === 'function'
     ? cancelAnimationFrame
     : clearImmediate;