Fix semicolon_if_nothing_returned clippy lint from PR 438

    warning: consider adding a `;` to the last statement for consistent formatting
       --> src/wrapper.rs:955:9
        |
    955 |         crate::fallback::invalidate_current_thread_spans()
        |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: add a `;` here: `crate::fallback::invalidate_current_thread_spans();`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_if_nothing_returned
        = note: `-W clippy::semicolon-if-nothing-returned` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::semicolon_if_nothing_returned)]`

Author: dtolnay

src/wrapper.rs

@@ -952,6 +952,6 @@ pub fn invalidate_current_thread_spans() {
             "proc_macro2::invalidate_current_thread_spans is not available in procedural macros"
         );
     } else {
-        crate::fallback::invalidate_current_thread_spans()
+        crate::fallback::invalidate_current_thread_spans();
     }
 }