conf-gnuplot: Try to fix

Author: clecat

packages/conf-gnuplot/conf-gnuplot.0.1/opam

@@ -4,7 +4,10 @@ homepage: "http://www.gnuplot.info/"
 authors: "http://www.gnuplot.info/faq/faq.html"
 bug-reports: "https://github.com/ocaml/opam-repository/issues"
 license: "gnuplot"
-build: ["gnuplot" "--version"]
+build: [
+  "gnuplot" "--version" { !(os = "win32" & os-distribution = "cygwin") }
+  "gnuplot-base.exe" "--version" {os = "win32" & os-distribution = "cygwin"}
+]
 depexts: [
   ["gnuplot-x11"] {os-family = "debian"}
   ["gnuplot-x11"] {os-family = "ubuntu"}