Replace str::trim_start with str::trim_left

std::trim_start was deprecated in Rust 1.33

src/input/priority_header.rs

@@ -128,7 +128,7 @@ impl<'a> Iterator for PriorityHeaderIter<'a> {
             let mut value = 1.0f32;
 
             for p in params {
-                let trimmed_p = p.trim_left();
+                let trimmed_p = p.trim_start();
                 if trimmed_p.starts_with("q=") {
                     if let Ok(val) = FromStr::from_str(&trimmed_p[2..].trim()) {
                         value = val; break;