fixup! Add a Config::set_once() function to set a value once (and let…

… Config::merge() overwrite it later

src/config.rs

@@ -151,7 +151,7 @@ impl Config {
         self.refresh()
     }
 
-    pub fn set_once<T>(&mut self, key: &str, value: Value) -> Result<()> {
+    pub fn set_once(&mut self, key: &str, value: Value) -> Result<()> {
         let expr: path::Expression = key.parse()?;
 
         // Traverse the cache using the path to (possibly) retrieve a value