style.9: Fix a typo (missing word)

Fixes:          af2c7d9f64 ("style.9: Encourage style changes when doing significant modifications")
MFC after:      1 day
Sponsored by:   The FreeBSD Foundation

share/man/man9/style.9

@@ -906,9 +906,9 @@ Their code is expected to at least be internally consistent with their style.
 Stylistic changes, including whitespace ones, complicate the work of downstream
 consumers and may impair developers' ability to trace the history of some
 changes.
-Such standalone must be avoided, and should not span unrelated directories as
-this increases the chances of conflicts when merging to stable and release
-branches (MFCs).
+Such standalone changes must be avoided, and should not span unrelated
+directories as this increases the chances of conflicts when merging to stable
+and release branches (MFCs).
 On the other hand, when a significant portion, usually about a half, of some
 logical unit of code, be it a function, group of functions, file or group of
 files, is going to be modified, developers are encouraged to amend the style of