Collected all clippy warnings and fixed 2

https://rust-lang.github.io/rust-clippy/master/index.html#inefficient_to_string
https://rust-lang.github.io/rust-clippy/master/index.html#match_wildcard_for_single_variants

Please change `allow` -> `deny` ub src/lib.rs to see other warnings. I feel some of them are important

src/context.rs

@@ -201,7 +201,7 @@ impl<'a> QueryPathNode<'a> {
         let mut res = Vec::new();
         self.for_each(|s| {
             res.push(match s {
-                QueryPathSegment::Name(name) => name.to_string(),
+                QueryPathSegment::Name(name) => (*name).to_string(),
                 QueryPathSegment::Index(idx) => idx.to_string(),
             });
         });

src/http/playground_source.rs

@@ -553,7 +553,7 @@ pub fn playground_source(config: GraphQLPlaygroundConfig) -> String {
 </html>
   "##.replace("GRAPHQL_PLAYGROUND_CONFIG", &match serde_json::to_string(&config) {
             Ok(str) => str,
-            _ => "{}".to_string()
+            Err(_) => "{}".to_string()
         })
 }
 

src/lib.rs

@@ -113,6 +113,40 @@
 //! Now a HTML report is available at `benchmark/target/criterion/report`.
 //!
 
+#![deny(clippy::all)]
+// #![deny(clippy::pedantic)]
+#![deny(clippy::inefficient_to_string)]
+#![deny(clippy::match_wildcard_for_single_variants)]
+#![allow(clippy::module_name_repetitions)]
+#![allow(clippy::similar_names)]
+#![allow(clippy::if_not_else)]
+#![allow(clippy::doc_markdown)]
+#![allow(clippy::must_use_candidate)]
+#![allow(clippy::missing_errors_doc)]
+#![allow(clippy::needless_pass_by_value)]
+#![allow(clippy::redundant_closure_for_method_calls)]
+#![allow(clippy::option_if_let_else)]
+#![allow(clippy::match_same_arms)]
+#![allow(clippy::filter_map)]
+#![allow(clippy::default_trait_access)]
+#![allow(clippy::map_flatten)]
+#![allow(clippy::map_unwrap_or)]
+#![allow(clippy::explicit_iter_loop)]
+#![allow(clippy::too_many_lines)]
+#![allow(clippy::cast_sign_loss)]
+#![allow(clippy::unused_self)]
+#![allow(clippy::find_map)]
+#![allow(clippy::cast_lossless)]
+#![allow(clippy::cast_possible_truncation)]
+#![allow(clippy::implicit_hasher)]
+// #![deny(clippy::nursery)]
+#![allow(clippy::use_self)]
+#![allow(clippy::missing_const_for_fn)]
+#![allow(clippy::needless_borrow)]
+#![allow(clippy::future_not_send)]
+#![allow(clippy::redundant_pub_crate)]
+#![allow(clippy::cognitive_complexity)]
+#![allow(clippy::useless_let_if_seq)]
 #![warn(missing_docs)]
 #![allow(clippy::trivially_copy_pass_by_ref)]
 #![recursion_limit = "256"]