Avoid unnecessary allocations.

src/api/json.rs

@@ -156,11 +156,13 @@ pub fn format_map_as_json(map: &Map) -> String {
     let mut result = String::from('{');
 
     for (key, value) in map {
+        use std::fmt::Write;
+
         if result.len() > 1 {
             result.push(',');
         }
 
-        result.push_str(&format!("{:?}", key));
+        write!(result, "{:?}", key).unwrap();
         result.push(':');
 
         if let Some(val) = value.read_lock::<Map>() {
@@ -171,7 +173,7 @@ pub fn format_map_as_json(map: &Map) -> String {
         if value.is::<()>() {
             result.push_str("null");
         } else {
-            result.push_str(&format!("{:?}", value));
+            write!(result, "{:?}", value).unwrap();
         }
     }