completion: fix misspelled config key aliasesfiletype

The correct name in git-send-email.perl is aliasfiletype [1]. There are actually two instances of this misspelling. The other was found and fixed in 6068ac8848 (completion: add missing configuration variables - 2010-12-20)

[1] 994d6c66d3 (send-email: address expansion for common mailers - 2006-05-14)

---
 contrib/completion/git-completion.bash | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 01dd9ff07a..bc8ce24a89 100644
@@ -2172,7 +2172,7 @@ _git_config ()
 		__gitcomp "$__git_log_date_formats"
 		return
 		;;
-	sendemail.aliasesfiletype)
+	sendemail.aliasfiletype)
 		__gitcomp "mutt mailrc pine elm gnus"
 		return
 		;;

2.17.0.705.g3525833791