Fix incorrect doc test {.should_panic} attribute

src/tags/media_segment/key.rs

@@ -117,7 +117,7 @@ impl<'a> ExtXKey<'a> {
     /// );
     /// ```
     ///
-    /// ```{.should_panic}
+    /// ```should_panic
     /// # use hls_m3u8::tags::ExtXKey;
     /// use hls_m3u8::types::DecryptionKey;
     ///

src/types/key_format_versions.rs

@@ -82,7 +82,7 @@ impl KeyFormatVersions {
     ///
     /// This will panic, because it exceeded the maximum number of elements:
     ///
-    /// ```{.should_panic}
+    /// ```should_panic
     /// # use hls_m3u8::types::KeyFormatVersions;
     /// let mut versions = KeyFormatVersions::new();
     ///