Fix test_missing_module_code_action_in_json_project on Windows

The test would fail on Windows due to the paths not being properly escaped for
JSON.

In addition adds extra braces around the fn main to actually introduce braces in
the file.

crates/ra_lsp_server/tests/heavy_tests/main.rs

@@ -263,20 +263,25 @@ fn main() {}
 #[test]
 fn test_missing_module_code_action_in_json_project() {
     let tmp_dir = TempDir::new().unwrap();
+
+    let path = tmp_dir.path();
+
+    let project = json!({
+        "roots": [path],
+        "crates": [ { "root_module": path.join("src/lib.rs"), "deps": [], "edition": "2015" } ]
+    });
+
     let code = format!(
         r#"
 //- rust-project.json
-{{ 
-    "roots": [ "{PATH}" ], 
-    "crates": [ {{ "root_module": "{PATH}/src/lib.rs", "deps": [], "edition": "2015" }} ] 
-}}
+{PROJECT}
 
 //- src/lib.rs
 mod bar;
 
-fn main() {}
+fn main() {{}}
 "#,
-        PATH = tmp_dir.path().display()
+        PROJECT = project.to_string(),
     );
     let server = project_with_tmpdir(tmp_dir, &code);
     server.wait_until_workspace_is_loaded();