Simple typo fix: Change "intarval" to "interval" (#1342)

Co-authored-by: Justin Starry <justin.starry@icloud.com>

yew/src/services/interval.rs

@@ -37,7 +37,7 @@ pub struct IntervalService {}
 
 impl IntervalService {
     /// Sets interval which will call send a messages returned by a converter
-    /// on every intarval expiration.
+    /// on every interval expiration.
     pub fn spawn(duration: Duration, callback: Callback<()>) -> IntervalTask {
         let callback = move || {
             callback.emit(());