patch 8.2.3914: various spelling mistakes in comments

Problem:    Various spelling mistakes in comments.
Solution:   Fix the mistakes. (Dominique Pellé, closes #9416)
diff --git a/src/os_mac.h b/src/os_mac.h
index 6524609..dbc0086 100644
--- a/src/os_mac.h
+++ b/src/os_mac.h
@@ -7,7 +7,7 @@
  */
 
 // Before Including the MacOS specific files,
-// lets set the OPAQUE_TOOLBOX_STRUCTS to 0 so we
+// let's set the OPAQUE_TOOLBOX_STRUCTS to 0 so we
 // can access the internal structures.
 // (Until fully Carbon compliant)
 // TODO: Can we remove this? (Dany)