lapce: fix derivation so that Lapce detects its version correctly

The build process of Lapce detects Lapce version
being built by reading `RELEASE_TAG_NAME`
environment variable.

It is then used, e.g., to download proper version
of `lapce-proxy` during remote development.

This commit sets this environment variable in
Lapce derivation.

Co-authored-by: Nick Cao <nickcao@nichi.co>

pkgs/applications/editors/lapce/default.nix

@@ -97,6 +97,9 @@ rustPlatform.buildRustPackage rec {
   # Get openssl-sys to use pkg-config
   OPENSSL_NO_VENDOR = 1;
 
+  # This variable is read by build script, so that Lapce editor knows its version
+  env.RELEASE_TAG_NAME = "v${version}";
+
   buildInputs = [
     glib
     gtk3