rust: use targetSubdir

lua/plugins/rustacean.lua

@@ -0,0 +1,15 @@
+return {
+  "mrcjkb/rustaceanvim",
+  opts = {
+    server = {
+      default_settings = {
+        -- rust-analyzer language server configuration
+        ["rust-analyzer"] = {
+          cargo = {
+            targetDir = true,
+          },
+        },
+      },
+    },
+  },
+}