patch 9.0.0828: various typos

Problem:    Various typos.
Solution:   Correct typos. (closes #11432)
diff --git a/src/proto/usercmd.pro b/src/proto/usercmd.pro
index 47ef6f0..d0cd2a3 100644
--- a/src/proto/usercmd.pro
+++ b/src/proto/usercmd.pro
@@ -18,7 +18,7 @@
 void ex_comclear(exarg_T *eap);
 void uc_clear(garray_T *gap);
 void ex_delcommand(exarg_T *eap);
-size_t add_win_cmd_modifers(char_u *buf, cmdmod_T *cmod, int *multi_mods);
+size_t add_win_cmd_modifiers(char_u *buf, cmdmod_T *cmod, int *multi_mods);
 size_t produce_cmdmods(char_u *buf, cmdmod_T *cmod, int quote);
 void do_ucmd(exarg_T *eap);
 /* vim: set ft=c : */