Fix lower bound of csexp in lsp

Suggestion provided by @mseri, thanks!

Author: Leonidas-from-XIV

packages/lsp/lsp.1.6.0/opam

@@ -23,7 +23,7 @@ depends: [
   "jsonrpc" {= version}
   "yojson"
   "ppx_yojson_conv_lib"
-  "csexp"
+  "csexp" {>= "1.4.0"}
   "uutf"
   "result" {>= "1.5"}
   "odoc" {with-doc}