plplot: typo on archlinux depext

See hcarty/ocaml-plplot#8

Author: mseri

packages/plplot/plplot.5.12.0/opam

@@ -21,7 +21,7 @@ depends: [
 depexts: [
   ["libplplot-dev" "libshp-dev"] {os-family = "debian"}
   ["plplot"] {os = "macos" & os-distribution = "homebrew"}
-  ["plpot"] {os-family = "arch"}
+  ["plplot"] {os-family = "arch"}
   ["plplot-devel"] {os-family = "rhel"}
   ["plplot-devel"] {os-family = "fedora"}
   ["plplot-devel"] {os-family = "suse"}