typo fix for vis.3

[Brooks Davis]

Kurt Jaeger submitted the following patch to vis.3 which we import into
FreeBSD from NetBSD.

-- Brooks

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=210013

--- contrib/libc-vis/vis.3 2016-06-04 06:46:24.234726000 +0200
+++ contrib/libc-vis/vis.3 2016-06-04 06:47:13.515516000 +0200
@@ -513,7 +513,7 @@
.Nx 6.0
and
.Fx 9.2 .
-Myltibyte character support was added in
+Multibyte character support was added in
.Nx 7.0
and
.Fx 9.2 .

[Thomas Klausner]

Post by Brooks Davis
Kurt Jaeger submitted the following patch to vis.3 which we import into
FreeBSD from NetBSD.

Thanks, fixed!
Thomas