Use push instead of extend_from_slice on chars

gen-dev-cargo-toml/src/main.rs

@@ -42,7 +42,7 @@ bin = [\n",
         buf.extend_from_slice(b"\", path = \"../exercises/");
         if let Some(dir) = &exercise_info.dir {
             buf.extend_from_slice(dir.as_bytes());
-            buf.extend_from_slice(b"/");
+            buf.push(b'/');
         }
         buf.extend_from_slice(exercise_info.name.as_bytes());
         buf.extend_from_slice(b".rs\" },\n");

src/app_state.rs

@@ -244,7 +244,7 @@ impl AppState {
         for exercise in &self.exercises {
             if exercise.done {
                 self.file_buf.extend_from_slice(exercise.name.as_bytes());
-                self.file_buf.extend_from_slice(b"\n");
+                self.file_buf.push(b'\n');
             }
         }
 

src/init.rs

@@ -17,7 +17,7 @@ fn create_cargo_toml(exercise_infos: &[ExerciseInfo]) -> io::Result<()> {
         cargo_toml.extend_from_slice(b"\", path = \"exercises/");
         if let Some(dir) = &exercise_info.dir {
             cargo_toml.extend_from_slice(dir.as_bytes());
-            cargo_toml.extend_from_slice(b"/");
+            cargo_toml.push(b'/');
         }
         cargo_toml.extend_from_slice(exercise_info.name.as_bytes());
         cargo_toml.extend_from_slice(b".rs\" },\n");