[doc] add a possessive apostrophe in OpenOptionsExt::mode

Author: cuviper

src/libstd/sys/unix/ext/fs.rs

@@ -306,7 +306,7 @@ pub trait OpenOptionsExt {
     /// If a new file is created as part of a `File::open_opts` call then this
     /// specified `mode` will be used as the permission bits for the new file.
     /// If no `mode` is set, the default of `0o666` will be used.
-    /// The operating system masks out bits with the systems `umask`, to produce
+    /// The operating system masks out bits with the system's `umask`, to produce
     /// the final permissions.
     ///
     /// # Examples

src/libstd/sys/vxworks/ext/fs.rs

@@ -307,7 +307,7 @@ pub trait OpenOptionsExt {
     /// If a new file is created as part of a `File::open_opts` call then this
     /// specified `mode` will be used as the permission bits for the new file.
     /// If no `mode` is set, the default of `0o666` will be used.
-    /// The operating system masks out bits with the systems `umask`, to produce
+    /// The operating system masks out bits with the system's `umask`, to produce
     /// the final permissions.
     ///
     /// # Examples